A) Passing itself to another method
B) Calling another constructor in constructor chaining
C) Referring to the instance variable when a local variable has the same name
D) Passing itself to the method of the same class
The correct answer is option D: “Passing itself to the method of the same class”. It is not the use of the “this” keyword in Java. Passing ‘this’ to methods within the same class is possible, but it’s not a unique use of the ‘this’ function.
Table of Contents:
What is the ‘this’ keyword in Java?
The ‘this’ keyword in Java refers to the current object. It helps you to refer to current objects inside the methods and constructors.
Why ‘Passing itself to the method of the same class’ is not the use of the ‘this’ keyword?
When you pass ‘this’ to the method of the same class, all you are doing is letting the method work with the current object.
It doesn’t add any special function that you couldn’t get by just directly passing object reference. For example, when you pass ‘this’ or any other object of the same type to the method, the method gets an object reference to work with. This is the basic part of how objects work in object-oriented programming.
Different Use Cases of ‘this’ Keyword in Java
1. Passing itself to another method using the ‘this’ keyword
In Java, when you use ‘this’ to pass the current object to another method, you are giving that method a reference to the current object. This is useful when you work with a current object in a different method.
Example: In the below example. we have used the ‘this’ keyword to pass the current object (this) to another method named displayValue within the same class.
public class Example {
private int value;
public Example(int value) {
this.value = value;
}
public void displayValue(Example obj) {
System.out.println("Value: " + obj.value);
}
public void showValue() {
this.displayValue(this);
}
public static void main(String[] args) {
Example ex = new Example(100);
ex.showValue();
}
}
Output
2. Calling another constructor in constructor chaining using the ‘this’ keyword
Constructor chaining means calling one constructor from another in the same class. When a class has multiple constructors, you can use ‘this’ to call one constructor from another. This helps you to avoid the code repetition.
Example: This example demonstrates constructor chaining. In this case, the Example() constructor calls the Example(int value) constructor, which in turn calls the Example(int value, int anotherValue) constructor using the ‘this’ keyword to avoid code repetition and initialize values.
public class Example {
private int value;
private int anotherValue;
public Example() {
this(10);
System.out.println("Default constructor called");
}
public Example(int value) {
this(value, 20);
System.out.println("Constructor with one parameter called");
}
public Example(int value, int anotherValue) {
this.value = value;
this.anotherValue = anotherValue;
System.out.println("Constructor with two parameters called");
}
public void display() {
System.out.println("Value: " + value);
System.out.println("Another Value: " + anotherValue);
}
public static void main(String[] args) {
Example ex = new Example();
ex.display();
}
}
Output
3. Referring to the instance variable when a local variable has the same name using the ‘this’ keyword
One of the main uses of ‘this’ in Java is to give the difference between the instance variable and local variable that have the same name. When a local variable has the same name as the instance variable, you can use the ‘this’ keyword to refer to the instance variable. Without ‘this’, Java would think you mean the local variable, and you wouldn’t be able to tell the difference between the instance and the local variable.
Example: This example demonstrates how the ‘this’ keyword is used to differentiate between an instance variable (value) and a local variable with the same name (value), ensuring the instance variable is referenced.
public class Example {
private int value;
public Example(int value) {
this.value = value;
}
public void displayValue() {
System.out.println("Value: " + this.value);
}
public static void main(String[] args) {
Example ex = new Example(100);
ex.displayValue();
}
}
Output
Conclusion
In Java, the `this` keyword is a powerful tool used to refer to the current object, differentiate between instance and local variables, and enable constructor chaining. However, passing `this` to methods within the same class does not have any special uses. Understanding the uses of `this` helps create more readable code.