Getter- og setter-metoder bruges ofte i Java-programmering. Getter og setter metoder i Java bruges i vid udstrækning til at få adgang til og manipulere værdierne af klassefelter. Normalt er klassefelter dekoreret med en privat adgangsspecifikation. For at få adgang til dem bruges specifikationer for offentlig adgang med getter- og setter-metoderne.
Behovet for Getter og Setter-metoden
Man kan argumentere for at erklære klassefelterne som offentlige og fjerne getter- og setter-metoderne. En sådan kodningsstil er dog dårlig, og man kan sætte en eller anden absurd værdi på klassefelterne. Lad os forstå det ved hjælp af et eksempel.
public class GetterSetterExample { public salary; public storeSalaryDB(int salary) { // code for storing the salary in the database } // main method public static void main(String argvs[]) { GetterSetterExample obj = new GetterSetterExample(); obj.salary = -50000; // storing salary in database obj.storeSalaryDB(salary); } } Bemærk, at koden gemmer en negativ løn i databasen, som er forkert. En organisation krediterer aldrig en negativ løn til en medarbejders konto. Tildeling af et absurd beløb til lønvariablen skete, fordi den er erklæret med en offentlig adgangsspecifikation. Den korrekte måde at skrive ovenstående kode på er:
public class GetterSetterExample { private salary; // a setter method that assign a // value to the salary variable void setSalary(int s) { if(s <0 ) { s="-s;" } this.salary="s;" a getter mehtod to retrieve the salary int getsalary() return this.salary; public storesalarydb(int salary) code for storing in database system.out.println('the ') main method static void main(string argvs[]) creating an object of class gettersetterexample obj="new" gettersetterexample(); obj.setsalary(-50000); obj.storesalarydb(salary); < pre> <p>Now, we can see better control over what we send to the database to store. Whenever the salary is negative, we are converting the salary into a positive value, and then we are sending it to the database to store. Thus, no matter what value we send to the setter method, the if-block of the setter method takes care of the absurd value and thus gives better control on the salary value.</p> <h2>Getter Setter Java Program</h2> <p> <strong>FileName:</strong> GetterSetterExample1.java</p> <pre> class Employee { // class member variable private int eId; private String eName; private String eDesignation; private String eCompany; public int getEmpId() { return eId; } public void setEmpId(final int eId) { this.eId = eId; } public String getEmpName() { return eName; } public void setEmpName(final String eName) { // Validating the employee's name and // throwing an exception if the name is null or its length is less than or equal to 0. if(eName == null || eName.length() <= 0) { throw new illegalargumentexception(); } this.ename="eName;" public string getempdesignation() return edesignation; void setempdesignation(final edesignation) this.edesignation="eDesignation;" getempcompany() ecompany; setempcompany(final ecompany) this.ecompany="eCompany;" for printing the values @override tostring() str="Employee: [id = " + getempid() ', name=" + getEmpName() + " , designation=" + getEmpDesignation() + " company=" + getEmpCompany() + " ]'; str; main class. class gettersetterexample1 method static main(string argvs[]) creating an object of employee final emp="new" employee(); details are getting set using setter methods. emp.setempid(107); emp.setempname('kathy'); emp.setempdesignation('software tester'); emp.setempcompany('xyz corporation'); displaying 'tostring()' method, which uses getter methods system.out.println(emp.tostring()); < pre> <p> <strong>Output:</strong> </p> <pre> Employee: [id = 107, name = Kathy, designation = Software Tester, company = XYZ Corporation] </pre> <h2>Bad Practices in Getter and Setter Methods</h2> <p>There are some common bad practices that people usually do when they deal with the getter and setter methods.</p> <h3>Bad Practice 1:</h3> <p>Using getter and setter for the variable that is declared with low restricted scope.</p> <pre> public salary; void setSalary(int s) { salary = s; } int getSalary() { return salary; } </pre> <p>It is evident that from the main method, one can directly access the variable salary, which is not only bad but also makes the presence of the getter and setter methods irrelevant.</p> <h3>Bad Practice 2:</h3> <p>Using an object reference in the setter method. Consider the following program.</p> <p> <strong>FileName:</strong> GetterSetterExample2.java</p> <pre> class ABC { private int[] val; void setVal(int[] arr) { this.val = arr; // line 7 } // for displaying the value // present in the val array void display() { int size = (this.val).length; for(int i = 0; i <size; i++) { system.out.print(this.val[i] + ' '); } main class public gettersetterexample2 method static void main(string argvs[]) instantiating the abc obj="new" abc(); int mainarr[]="{3," 4, 6, 8, 78, 9}; invoking setter obj.setval(mainarr); display obj.display(); updating value at 0th index mainarr[0]="-1;" system.out.println(); < pre> <p> <strong>Output:</strong> </p> <pre> 3 4 6 8 78 9 -1 4 6 8 78 9 </pre> <p> <strong>Explanation:</strong> </p> <p>References are a bit tricky to deal with! In the above code, at line 43, the value got updated at the 0th index for array mainArr[]. However, it also got reflected in the array val[]. It should not happen as val[] array is declared private; hence, it is expected that any code outside of the class ABC should not modify it. However, because of the references, everything is messed up. The setter method setVal() expecting a reference of an int array, and at line 7, the reference of the int arr[] is getting copied to val[]. Note that the reference variable arr[] is storing the reference of the array mainArr[]. Thus, we can say val[] is storing the reference of the mainArr[].</p> <p>Therefore, whatever we change in the mainArr[] also gets reflected in the val[] array, which violates the purpose of the setter method. Also, there is no meaning in adding the private access specifier to the val[] array; because one can change the value of the val[] array in the main method, which is evident by looking at the output.</p> <p>A better way of writing the above code is:</p> <p> <strong>FileName:</strong> GetterSetterExample3.java</p> <pre> class ABC { private int[] val; void setVal(int[] arr) { int size = arr.length; // allocating the memory as // per the array arr size val = new int[size]; // line 11 for(int i = 0; i <size; 17 53 i++) { copying the value one by into val array this.val[i]="arr[i];" line } for displaying present in void display() int size="(this.val).length;" for(int i="0;" < size; system.out.print(this.val[i] + ' '); main class. public class gettersetterexample3 method static main(string argvs[]) instantiating abc obj="new" abc(); mainarr[]="{3," 4, 6, 8, 78, 9}; invoking setter obj.setval(mainarr); display obj.display(); updating at 0th index mainarr[0]="-1;" system.out.println(); again pre> <p> <strong>Output:</strong> </p> <pre> 3 4 6 8 78 9 3 4 6 8 78 9 </pre> <p> <strong>Explanation:</strong> </p> <p>In the above code, we are doing the deep copy of elements of the array arr[]. In line 11, we are creating an entirely new array. Thus, the val[] is not referring to the arr[]. Also, in line 17, only values of the element are getting copied. Therefore, when we change the value of the 0th element at line 53, the change is not reflected in the val[]. Thus, the above code respects the encapsulation of the private member variable val[].</p> <h3>Bad Practice 3:</h3> <p>Returning an object reference in the getter method. Observe the following program.</p> <p> <strong>FileName:</strong> GetterSetterExample4.java</p> <pre> class ABC { private int[] val = {67, 43, 68, 112, 70, 12}; // the getter method public int[] getVal() { // returning the reference return val; // line 9 } // for displaying the value // present in the val array void display() { int size = (this.val).length; for(int i = 0; i <size; 42 i++) { system.out.print(this.val[i] + ' '); } main class. public class gettersetterexample4 method static void main(string argvs[]) instantiating the abc obj="new" abc(); invoking getter and storing result int arr[]="obj.getVal();" display obj.display(); updating value at 0th index arr[0]="-1;" line system.out.println(); again < pre> <p> <strong>Output:</strong> </p> <pre> 67 43 68 112 70 12 -1 43 68 112 70 12 </pre> <p> <strong>Explanation:</strong> </p> <p>The above code is not handling the references properly. The getter method is returning the reference of the array. The arr[] is storing the reference of the array val[], which is declared private in the class ABC. Because of exposing the reference to the outer world, arr[] can manipulate the val[], and thus, the encapsulation of the class ABC is breached. The proper way to handle the above is:</p> <p> <strong>FileName:</strong> GetterSetterExample5.java</p> <pre> class ABC { private int[] val = {67, 43, 68, 112, 70, 12}; // the getter method public int[] getVal() { int size = val.length; // creating a new array int temp[] = new int[size]; // copying the content of the array to temp array for(int i = 0; i <size; 54 i++) { temp[i]="val[i];" } return temp; for displaying the value present in val array void display() int size="(this.val).length;" for(int i="0;" < size; system.out.print(this.val[i] + ' '); main class. public class gettersetterexample5 method static main(string argvs[]) instantiating abc obj="new" abc(); invoking getter and storing result arr[]="obj.getVal();" display obj.display(); updating at 0th index arr[0]="-1;" line system.out.println(); pre> <p> <strong>Output:</strong> </p> <pre> 67 43 68 112 70 12 67 43 68 112 70 12 </pre> <p> <strong>Explanation:</strong> In the above code, the reference of the private array is not sent to the outside world. In the getter method, a new array is created whose reference is sent to the main method. Therefore, when the value at the 0th index gets changed at line 54, that change impacts the temp[] array, not the private array val[]. Thus, the encapsulation of the class ABC is maintained, as the reference of the array val[] is not exposed to the outside world.</p> <h4>Note 1: For primitive data types (int, char, etc.), one does not need to create a copy in the getter and setter methods, as the concept of references is absent for the primitive data types.</h4> <h4>Note 2: Strings object types also work on the references. However, unlike the above examples, one does not need to take care of the String references exposed to the outside world. It is because Strings are immutable. Thus, when one manipulates the string in the main method (or anywhere else), a new String object is created, and the previous one remains untouched.</h4> <p> <strong>FileName:</strong> GetterSetterExample6.java</p> <pre> class ABC { private String str = null; // a setter method void setVal(String s) { // reference is getting copied this.str = s; } // for displaying the string void display() { System.out.println( 'The String is: ' + this.str); } } // Main class. public class GetterSetterExample6 { // main method public static void main(String argvs[]) { // creating an object of the class ABC ABC obj = new ABC(); // input string String inputStr = 'Hello India!'; // invoking the setter method obj.setVal(inputStr); obj.display(); // manipulation is not allowed! // it leads to the creation of the new string inputStr = 'Hello World!'; obj.display(); } } </pre> <p> <strong>Output:</strong> </p> <pre> The String is: Hello India! The String is: Hello India! </pre> <hr></size;></pre></size;></pre></size;></pre></size;></pre></=></pre></0> Dårlig praksis i Getter- og Setter-metoder
Der er nogle almindelige dårlige praksisser, som folk normalt gør, når de beskæftiger sig med getter- og setter-metoderne.
Dårlig praksis 1:
Brug af getter og setter til den variabel, der er deklareret med lavt begrænset omfang.
public salary; void setSalary(int s) { salary = s; } int getSalary() { return salary; } Det er tydeligt, at man fra hovedmetoden kan få direkte adgang til den variable løn, hvilket ikke kun er dårligt, men også gør tilstedeværelsen af getter- og setter-metoderne irrelevant.
Dårlig praksis 2:
Brug af en objektreference i setter-metoden. Overvej følgende program.
Filnavn: GetterSetterExample2.java
class ABC { private int[] val; void setVal(int[] arr) { this.val = arr; // line 7 } // for displaying the value // present in the val array void display() { int size = (this.val).length; for(int i = 0; i <size; i++) { system.out.print(this.val[i] + \' \'); } main class public gettersetterexample2 method static void main(string argvs[]) instantiating the abc obj="new" abc(); int mainarr[]="{3," 4, 6, 8, 78, 9}; invoking setter obj.setval(mainarr); display obj.display(); updating value at 0th index mainarr[0]="-1;" system.out.println(); < pre> <p> <strong>Output:</strong> </p> <pre> 3 4 6 8 78 9 -1 4 6 8 78 9 </pre> <p> <strong>Explanation:</strong> </p> <p>References are a bit tricky to deal with! In the above code, at line 43, the value got updated at the 0th index for array mainArr[]. However, it also got reflected in the array val[]. It should not happen as val[] array is declared private; hence, it is expected that any code outside of the class ABC should not modify it. However, because of the references, everything is messed up. The setter method setVal() expecting a reference of an int array, and at line 7, the reference of the int arr[] is getting copied to val[]. Note that the reference variable arr[] is storing the reference of the array mainArr[]. Thus, we can say val[] is storing the reference of the mainArr[].</p> <p>Therefore, whatever we change in the mainArr[] also gets reflected in the val[] array, which violates the purpose of the setter method. Also, there is no meaning in adding the private access specifier to the val[] array; because one can change the value of the val[] array in the main method, which is evident by looking at the output.</p> <p>A better way of writing the above code is:</p> <p> <strong>FileName:</strong> GetterSetterExample3.java</p> <pre> class ABC { private int[] val; void setVal(int[] arr) { int size = arr.length; // allocating the memory as // per the array arr size val = new int[size]; // line 11 for(int i = 0; i <size; 17 53 i++) { copying the value one by into val array this.val[i]="arr[i];" line } for displaying present in void display() int size="(this.val).length;" for(int i="0;" < size; system.out.print(this.val[i] + \' \'); main class. public class gettersetterexample3 method static main(string argvs[]) instantiating abc obj="new" abc(); mainarr[]="{3," 4, 6, 8, 78, 9}; invoking setter obj.setval(mainarr); display obj.display(); updating at 0th index mainarr[0]="-1;" system.out.println(); again pre> <p> <strong>Output:</strong> </p> <pre> 3 4 6 8 78 9 3 4 6 8 78 9 </pre> <p> <strong>Explanation:</strong> </p> <p>In the above code, we are doing the deep copy of elements of the array arr[]. In line 11, we are creating an entirely new array. Thus, the val[] is not referring to the arr[]. Also, in line 17, only values of the element are getting copied. Therefore, when we change the value of the 0th element at line 53, the change is not reflected in the val[]. Thus, the above code respects the encapsulation of the private member variable val[].</p> <h3>Bad Practice 3:</h3> <p>Returning an object reference in the getter method. Observe the following program.</p> <p> <strong>FileName:</strong> GetterSetterExample4.java</p> <pre> class ABC { private int[] val = {67, 43, 68, 112, 70, 12}; // the getter method public int[] getVal() { // returning the reference return val; // line 9 } // for displaying the value // present in the val array void display() { int size = (this.val).length; for(int i = 0; i <size; 42 i++) { system.out.print(this.val[i] + \' \'); } main class. public class gettersetterexample4 method static void main(string argvs[]) instantiating the abc obj="new" abc(); invoking getter and storing result int arr[]="obj.getVal();" display obj.display(); updating value at 0th index arr[0]="-1;" line system.out.println(); again < pre> <p> <strong>Output:</strong> </p> <pre> 67 43 68 112 70 12 -1 43 68 112 70 12 </pre> <p> <strong>Explanation:</strong> </p> <p>The above code is not handling the references properly. The getter method is returning the reference of the array. The arr[] is storing the reference of the array val[], which is declared private in the class ABC. Because of exposing the reference to the outer world, arr[] can manipulate the val[], and thus, the encapsulation of the class ABC is breached. The proper way to handle the above is:</p> <p> <strong>FileName:</strong> GetterSetterExample5.java</p> <pre> class ABC { private int[] val = {67, 43, 68, 112, 70, 12}; // the getter method public int[] getVal() { int size = val.length; // creating a new array int temp[] = new int[size]; // copying the content of the array to temp array for(int i = 0; i <size; 54 i++) { temp[i]="val[i];" } return temp; for displaying the value present in val array void display() int size="(this.val).length;" for(int i="0;" < size; system.out.print(this.val[i] + \' \'); main class. public class gettersetterexample5 method static main(string argvs[]) instantiating abc obj="new" abc(); invoking getter and storing result arr[]="obj.getVal();" display obj.display(); updating at 0th index arr[0]="-1;" line system.out.println(); pre> <p> <strong>Output:</strong> </p> <pre> 67 43 68 112 70 12 67 43 68 112 70 12 </pre> <p> <strong>Explanation:</strong> In the above code, the reference of the private array is not sent to the outside world. In the getter method, a new array is created whose reference is sent to the main method. Therefore, when the value at the 0th index gets changed at line 54, that change impacts the temp[] array, not the private array val[]. Thus, the encapsulation of the class ABC is maintained, as the reference of the array val[] is not exposed to the outside world.</p> <h4>Note 1: For primitive data types (int, char, etc.), one does not need to create a copy in the getter and setter methods, as the concept of references is absent for the primitive data types.</h4> <h4>Note 2: Strings object types also work on the references. However, unlike the above examples, one does not need to take care of the String references exposed to the outside world. It is because Strings are immutable. Thus, when one manipulates the string in the main method (or anywhere else), a new String object is created, and the previous one remains untouched.</h4> <p> <strong>FileName:</strong> GetterSetterExample6.java</p> <pre> class ABC { private String str = null; // a setter method void setVal(String s) { // reference is getting copied this.str = s; } // for displaying the string void display() { System.out.println( 'The String is: ' + this.str); } } // Main class. public class GetterSetterExample6 { // main method public static void main(String argvs[]) { // creating an object of the class ABC ABC obj = new ABC(); // input string String inputStr = 'Hello India!'; // invoking the setter method obj.setVal(inputStr); obj.display(); // manipulation is not allowed! // it leads to the creation of the new string inputStr = 'Hello World!'; obj.display(); } } </pre> <p> <strong>Output:</strong> </p> <pre> The String is: Hello India! The String is: Hello India! </pre> <hr></size;></pre></size;></pre></size;></pre></size;> Forklaring:
Referencer er lidt vanskelige at håndtere! I ovenstående kode, på linje 43, blev værdien opdateret ved det 0. indeks for array mainArr[]. Det blev dog også afspejlet i array val[]. Det bør ikke ske, da val[] array er erklæret privat; derfor forventes det, at enhver kode uden for klassen ABC ikke bør ændre den. Men på grund af referencerne er alt rodet. Setter-metoden setVal() forventer en reference for et int-array, og på linje 7 bliver referencen for int arr[] kopieret til val[]. Bemærk, at referencevariablen arr[] gemmer referencen for arrayet mainArr[]. Således kan vi sige, at val[] gemmer referencen til mainArr[].
Derfor bliver hvad end vi ændrer i mainArr[] også afspejlet i val[]-arrayet, hvilket overtræder formålet med setter-metoden. Desuden er der ingen mening med at tilføje den private adgangsspecifikation til val[]-arrayet; fordi man kan ændre værdien af val[]-arrayet i hovedmetoden, hvilket er tydeligt ved at se på outputtet.
En bedre måde at skrive ovenstående kode på er:
osi model lag
Filnavn: GetterSetterExample3.java
class ABC { private int[] val; void setVal(int[] arr) { int size = arr.length; // allocating the memory as // per the array arr size val = new int[size]; // line 11 for(int i = 0; i <size; 17 53 i++) { copying the value one by into val array this.val[i]="arr[i];" line } for displaying present in void display() int size="(this.val).length;" for(int i="0;" < size; system.out.print(this.val[i] + \' \'); main class. public class gettersetterexample3 method static main(string argvs[]) instantiating abc obj="new" abc(); mainarr[]="{3," 4, 6, 8, 78, 9}; invoking setter obj.setval(mainarr); display obj.display(); updating at 0th index mainarr[0]="-1;" system.out.println(); again pre> <p> <strong>Output:</strong> </p> <pre> 3 4 6 8 78 9 3 4 6 8 78 9 </pre> <p> <strong>Explanation:</strong> </p> <p>In the above code, we are doing the deep copy of elements of the array arr[]. In line 11, we are creating an entirely new array. Thus, the val[] is not referring to the arr[]. Also, in line 17, only values of the element are getting copied. Therefore, when we change the value of the 0th element at line 53, the change is not reflected in the val[]. Thus, the above code respects the encapsulation of the private member variable val[].</p> <h3>Bad Practice 3:</h3> <p>Returning an object reference in the getter method. Observe the following program.</p> <p> <strong>FileName:</strong> GetterSetterExample4.java</p> <pre> class ABC { private int[] val = {67, 43, 68, 112, 70, 12}; // the getter method public int[] getVal() { // returning the reference return val; // line 9 } // for displaying the value // present in the val array void display() { int size = (this.val).length; for(int i = 0; i <size; 42 i++) { system.out.print(this.val[i] + \' \'); } main class. public class gettersetterexample4 method static void main(string argvs[]) instantiating the abc obj="new" abc(); invoking getter and storing result int arr[]="obj.getVal();" display obj.display(); updating value at 0th index arr[0]="-1;" line system.out.println(); again < pre> <p> <strong>Output:</strong> </p> <pre> 67 43 68 112 70 12 -1 43 68 112 70 12 </pre> <p> <strong>Explanation:</strong> </p> <p>The above code is not handling the references properly. The getter method is returning the reference of the array. The arr[] is storing the reference of the array val[], which is declared private in the class ABC. Because of exposing the reference to the outer world, arr[] can manipulate the val[], and thus, the encapsulation of the class ABC is breached. The proper way to handle the above is:</p> <p> <strong>FileName:</strong> GetterSetterExample5.java</p> <pre> class ABC { private int[] val = {67, 43, 68, 112, 70, 12}; // the getter method public int[] getVal() { int size = val.length; // creating a new array int temp[] = new int[size]; // copying the content of the array to temp array for(int i = 0; i <size; 54 i++) { temp[i]="val[i];" } return temp; for displaying the value present in val array void display() int size="(this.val).length;" for(int i="0;" < size; system.out.print(this.val[i] + \' \'); main class. public class gettersetterexample5 method static main(string argvs[]) instantiating abc obj="new" abc(); invoking getter and storing result arr[]="obj.getVal();" display obj.display(); updating at 0th index arr[0]="-1;" line system.out.println(); pre> <p> <strong>Output:</strong> </p> <pre> 67 43 68 112 70 12 67 43 68 112 70 12 </pre> <p> <strong>Explanation:</strong> In the above code, the reference of the private array is not sent to the outside world. In the getter method, a new array is created whose reference is sent to the main method. Therefore, when the value at the 0th index gets changed at line 54, that change impacts the temp[] array, not the private array val[]. Thus, the encapsulation of the class ABC is maintained, as the reference of the array val[] is not exposed to the outside world.</p> <h4>Note 1: For primitive data types (int, char, etc.), one does not need to create a copy in the getter and setter methods, as the concept of references is absent for the primitive data types.</h4> <h4>Note 2: Strings object types also work on the references. However, unlike the above examples, one does not need to take care of the String references exposed to the outside world. It is because Strings are immutable. Thus, when one manipulates the string in the main method (or anywhere else), a new String object is created, and the previous one remains untouched.</h4> <p> <strong>FileName:</strong> GetterSetterExample6.java</p> <pre> class ABC { private String str = null; // a setter method void setVal(String s) { // reference is getting copied this.str = s; } // for displaying the string void display() { System.out.println( 'The String is: ' + this.str); } } // Main class. public class GetterSetterExample6 { // main method public static void main(String argvs[]) { // creating an object of the class ABC ABC obj = new ABC(); // input string String inputStr = 'Hello India!'; // invoking the setter method obj.setVal(inputStr); obj.display(); // manipulation is not allowed! // it leads to the creation of the new string inputStr = 'Hello World!'; obj.display(); } } </pre> <p> <strong>Output:</strong> </p> <pre> The String is: Hello India! The String is: Hello India! </pre> <hr></size;></pre></size;></pre></size;> Forklaring:
I ovenstående kode laver vi den dybe kopi af elementer i arrayet arr[]. I linje 11 skaber vi et helt nyt array. Således refererer val[] ikke til arr[]. Også i linje 17 bliver kun værdier af elementet kopieret. Derfor, når vi ændrer værdien af det 0. element på linje 53, afspejles ændringen ikke i val[]. Ovenstående kode respekterer således indkapslingen af den private medlemsvariabel val[].
Dårlig praksis 3:
Returnerer en objektreference i getter-metoden. Overhold følgende program.
Filnavn: GetterSetterExample4.java
class ABC { private int[] val = {67, 43, 68, 112, 70, 12}; // the getter method public int[] getVal() { // returning the reference return val; // line 9 } // for displaying the value // present in the val array void display() { int size = (this.val).length; for(int i = 0; i <size; 42 i++) { system.out.print(this.val[i] + \' \'); } main class. public class gettersetterexample4 method static void main(string argvs[]) instantiating the abc obj="new" abc(); invoking getter and storing result int arr[]="obj.getVal();" display obj.display(); updating value at 0th index arr[0]="-1;" line system.out.println(); again < pre> <p> <strong>Output:</strong> </p> <pre> 67 43 68 112 70 12 -1 43 68 112 70 12 </pre> <p> <strong>Explanation:</strong> </p> <p>The above code is not handling the references properly. The getter method is returning the reference of the array. The arr[] is storing the reference of the array val[], which is declared private in the class ABC. Because of exposing the reference to the outer world, arr[] can manipulate the val[], and thus, the encapsulation of the class ABC is breached. The proper way to handle the above is:</p> <p> <strong>FileName:</strong> GetterSetterExample5.java</p> <pre> class ABC { private int[] val = {67, 43, 68, 112, 70, 12}; // the getter method public int[] getVal() { int size = val.length; // creating a new array int temp[] = new int[size]; // copying the content of the array to temp array for(int i = 0; i <size; 54 i++) { temp[i]="val[i];" } return temp; for displaying the value present in val array void display() int size="(this.val).length;" for(int i="0;" < size; system.out.print(this.val[i] + \' \'); main class. public class gettersetterexample5 method static main(string argvs[]) instantiating abc obj="new" abc(); invoking getter and storing result arr[]="obj.getVal();" display obj.display(); updating at 0th index arr[0]="-1;" line system.out.println(); pre> <p> <strong>Output:</strong> </p> <pre> 67 43 68 112 70 12 67 43 68 112 70 12 </pre> <p> <strong>Explanation:</strong> In the above code, the reference of the private array is not sent to the outside world. In the getter method, a new array is created whose reference is sent to the main method. Therefore, when the value at the 0th index gets changed at line 54, that change impacts the temp[] array, not the private array val[]. Thus, the encapsulation of the class ABC is maintained, as the reference of the array val[] is not exposed to the outside world.</p> <h4>Note 1: For primitive data types (int, char, etc.), one does not need to create a copy in the getter and setter methods, as the concept of references is absent for the primitive data types.</h4> <h4>Note 2: Strings object types also work on the references. However, unlike the above examples, one does not need to take care of the String references exposed to the outside world. It is because Strings are immutable. Thus, when one manipulates the string in the main method (or anywhere else), a new String object is created, and the previous one remains untouched.</h4> <p> <strong>FileName:</strong> GetterSetterExample6.java</p> <pre> class ABC { private String str = null; // a setter method void setVal(String s) { // reference is getting copied this.str = s; } // for displaying the string void display() { System.out.println( 'The String is: ' + this.str); } } // Main class. public class GetterSetterExample6 { // main method public static void main(String argvs[]) { // creating an object of the class ABC ABC obj = new ABC(); // input string String inputStr = 'Hello India!'; // invoking the setter method obj.setVal(inputStr); obj.display(); // manipulation is not allowed! // it leads to the creation of the new string inputStr = 'Hello World!'; obj.display(); } } </pre> <p> <strong>Output:</strong> </p> <pre> The String is: Hello India! The String is: Hello India! </pre> <hr></size;></pre></size;> Forklaring:
Ovenstående kode håndterer ikke referencerne korrekt. Getter-metoden returnerer referencen for arrayet. arr[] gemmer referencen for array val[], som er erklæret privat i klassen ABC. På grund af at afsløre referencen til den ydre verden, kan arr[] manipulere val[], og dermed bliver indkapslingen af klassen ABC brudt. Den korrekte måde at håndtere ovenstående på er:
Filnavn: GetterSetterExample5.java
class ABC { private int[] val = {67, 43, 68, 112, 70, 12}; // the getter method public int[] getVal() { int size = val.length; // creating a new array int temp[] = new int[size]; // copying the content of the array to temp array for(int i = 0; i <size; 54 i++) { temp[i]="val[i];" } return temp; for displaying the value present in val array void display() int size="(this.val).length;" for(int i="0;" < size; system.out.print(this.val[i] + \\' \\'); main class. public class gettersetterexample5 method static main(string argvs[]) instantiating abc obj="new" abc(); invoking getter and storing result arr[]="obj.getVal();" display obj.display(); updating at 0th index arr[0]="-1;" line system.out.println(); pre> <p> <strong>Output:</strong> </p> <pre> 67 43 68 112 70 12 67 43 68 112 70 12 </pre> <p> <strong>Explanation:</strong> In the above code, the reference of the private array is not sent to the outside world. In the getter method, a new array is created whose reference is sent to the main method. Therefore, when the value at the 0th index gets changed at line 54, that change impacts the temp[] array, not the private array val[]. Thus, the encapsulation of the class ABC is maintained, as the reference of the array val[] is not exposed to the outside world.</p> <h4>Note 1: For primitive data types (int, char, etc.), one does not need to create a copy in the getter and setter methods, as the concept of references is absent for the primitive data types.</h4> <h4>Note 2: Strings object types also work on the references. However, unlike the above examples, one does not need to take care of the String references exposed to the outside world. It is because Strings are immutable. Thus, when one manipulates the string in the main method (or anywhere else), a new String object is created, and the previous one remains untouched.</h4> <p> <strong>FileName:</strong> GetterSetterExample6.java</p> <pre> class ABC { private String str = null; // a setter method void setVal(String s) { // reference is getting copied this.str = s; } // for displaying the string void display() { System.out.println( 'The String is: ' + this.str); } } // Main class. public class GetterSetterExample6 { // main method public static void main(String argvs[]) { // creating an object of the class ABC ABC obj = new ABC(); // input string String inputStr = 'Hello India!'; // invoking the setter method obj.setVal(inputStr); obj.display(); // manipulation is not allowed! // it leads to the creation of the new string inputStr = 'Hello World!'; obj.display(); } } </pre> <p> <strong>Output:</strong> </p> <pre> The String is: Hello India! The String is: Hello India! </pre> <hr></size;> Forklaring: I ovenstående kode sendes referencen for det private array ikke til omverdenen. I getter-metoden oprettes et nyt array, hvis reference sendes til hovedmetoden. Derfor, når værdien ved det 0. indeks bliver ændret på linje 54, påvirker denne ændring temp[]-arrayet, ikke den private array-værdi[]. Dermed opretholdes indkapslingen af klassen ABC, da referencen for array val[] ikke er udsat for omverdenen.
Note 1: For primitive datatyper (int, char osv.) behøver man ikke at oprette en kopi i getter- og setter-metoderne, da referencebegrebet er fraværende for de primitive datatyper.
Note 2: Strings objekttyper fungerer også på referencerne. Men i modsætning til ovenstående eksempler behøver man ikke at tage sig af de String-referencer, der er udsat for omverdenen. Det er fordi strenge er uforanderlige. Når man manipulerer strengen i hovedmetoden (eller et hvilket som helst andet sted), oprettes et nyt String-objekt, og det forrige forbliver urørt.
Filnavn: GetterSetterExample6.java
class ABC { private String str = null; // a setter method void setVal(String s) { // reference is getting copied this.str = s; } // for displaying the string void display() { System.out.println( 'The String is: ' + this.str); } } // Main class. public class GetterSetterExample6 { // main method public static void main(String argvs[]) { // creating an object of the class ABC ABC obj = new ABC(); // input string String inputStr = 'Hello India!'; // invoking the setter method obj.setVal(inputStr); obj.display(); // manipulation is not allowed! // it leads to the creation of the new string inputStr = 'Hello World!'; obj.display(); } } Produktion:
The String is: Hello India! The String is: Hello India!