What is multiple inheritance? Does Java support multiple inheritance?

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The this keyword in Java is a reference variable that refers to the current object, the object whose method or constructor is being called. It is used within an instance method or a constructor to refer to the current object.

Uses of the this Keyword

1. Referring to Instance Variables:

  • this is commonly used to differentiate between instance variables (fields) and parameters or other variables that have the same name.

Example:

```java

class Example {

int number;

   Example(int number) {
       this.number = number; // 'this.number' refers to the instance variable, 'number' refers to the parameter
   }
void display() {  

System.out.println("Number: " + this.number);


}

}

public class Main {

public static void main(String[] args) {

Example example \= new Example(5);

example.display(); // Output: Number: 5

}

} 

 In this example,`this.number`refers to the instance variable`number`, while the plain`number\` refers to the constructor's parameter.

2. Invoking Current Class Methods:


    

  • this can be used to call another method of the current class. It is optional but can be used for clarity.
    • 



Example:


```java


class Example {


void method1() {


System.out.println("Method 1 called");


this.method2(); // Calling method2 of the current class


}

void method2() {
System.out.println("Method 2 called");
}


}

public class Main {


public static void main(String args) {


Example example = new Example();


example.method1();


}


}


**Output**:


Method 1 called


Method 2 called


```


3. Invoking Current Class Constructors:


    

  • this() can be used to invoke a constructor of the current class. It helps in constructor chaining, where one constructor calls another constructor in the same class.
    • 



Example:


```java


class Example {


Example() {


this(10); // Calls the parameterized constructor


System.out.println("Default constructor called");


}

Example(int number) {
System.out.println("Parameterized constructor called with value: " + number);
}


}

public class Main {


public static void main(String args) {


Example example = new Example();


}


}


**Output**:


Parameterized constructor called with value: 10


Default constructor called


```


4. Returning Current Class Instance:


    

  • this can be used to return the current class instance from a method. This is often used in method chaining.
    • 



Example:


```java


class Example {


int number;

Example setNumber(int number) {
this.number = number;
return this; // Returns current class instance
}
void display() {

System.out.println("Number: " + number);

}

```

}

public class Main {

public static void main(String[] args) {

Example example \= new Example();

example.setNumber(10).display(); // Method chaining

}

}

**Output**:

Number: 10

```

Summary of this Keyword

  • Purpose: this is used to refer to the current object within an instance method or a constructor.
  • Main Uses:
  • To refer to the instance variables of the current object, especially when they are shadowed by method or constructor parameters.
  • To invoke the current class's methods.
  • To call a constructor from another constructor in the same class (constructor chaining).
  • To return the current class instance, facilitating method chaining.