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home / developersection / forums / what is this keyword in java?
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Krishnapriya Rajeev
Krishnapriya Rajeev

Student

I am a Computer Science Engineering student currently in the sixth semester of my B.Tech. program. My interests lie in the areas of machine learning and deep learning and I am also familiar with programming languages such as C, C++, Java, and Python.

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2 Answers

Aryan Kumar
Aryan Kumar 01 May 2023
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In Java, this is a keyword that refers to the current object or instance of a class. It is used to refer to the current object's instance variables, methods, and constructors.

Here are some common uses of the this keyword in Java:

  • To refer to instance variables: When an instance variable has the same name as a parameter or local variable in a method, the this keyword can be used to distinguish between the two. For example:
public class Person {
   private String name;
   public Person(String name) {
       this.name = name;
   }
   public void setName(String name) {
       this.name = name; // Use this.name to refer to the instance variable
   }
}
  • To call another constructor in the same class: When a class has multiple constructors, one constructor can call another constructor using the this keyword. The called constructor must be the first statement in the calling constructor. For example:
public class Person {
   private String name;
   private int age;
   public Person(String name) {
       this(name, 0); // Call the two-argument constructor with age = 0
   }
   public Person(String name, int age) {
       this.name = name;
       this.age = age;
   }
}
  • To return the current object from a method: In some cases, a method needs to return the current object to allow method chaining. This can be done by returning this. For example:
public class Person {
   private String name;
   private int age;
   public Person setName(String name) {
       this.name = name;
       return this; // Return the current object to allow method chaining
   }
   public Person setAge(int age) {
       this.age = age;
       return this; // Return the current object to allow method chaining
   }
}

The this keyword can also be used in other contexts, such as to pass the current object as a parameter to another method or to synchronize on the current object.


 

Krishnapriya Rajeev
Krishnapriya Rajeev 29 Apr 2023
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In Java, "this" is a keyword that refers to the current instance of the class in which it is used. It used in the following ways:

  • In a method or constructor of a class, "this" can be used to refer to instance variables of the class. For example, "this.name" would refer to the "name" instance variable of the current instance of the class.
  •  A constructor can use "this" to invoke another constructor of the same class. This is useful when the same initialization code needs to be called from multiple constructors. The call to the other constructor must be the first statement in the constructor.
  • In a method of a class, "this" can be used to return the current instance of the class. This is useful when chaining method calls or when returning the current object from a method.
  • "this" can be used to pass the current instance of the class as a parameter to another method. This is useful when a method needs to access the state of the current instance of the class.

For example, consider the following class:

public class Person {
    private String name;

    public Person(String name) {
        this.name = name;
    }

    public String getName() {
        return this.name;
    }
}

In the constructor, "this.name" refers to the instance variable "name" of the current instance of the class. In the "getName" method, "this" is used to return the current instance of the class.

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