this keyword

In Java, this is a keyword that refers to the current object — the object on which the method or constructor is being called.

In simple words: this means "myself" (the current object).

Why do we need this?

Let’s say you have a variable called name, and you also pass a parameter named name to a constructor. How will Java know which one you're talking about?

That’s where this comes in.

Example 1: When variable names are the same

public class Student {
    String name;
    Student(String name) {
        this.name = name; // 'this.name' refers to instance variable
      // whereas name refers to parameter
    }
    void display() {
        System.out.println("Name: " + this.name);
    }
}

Output:

Name: Rahul

In the constructor, this.name refers to the variable inside the class, and name is the parameter passed to the constructor.

Example 2: Calling another constructor using this()

You can use this() to call another constructor from the same class.

public class Student {
    String name;
    int age;
    Student() {
        this("Default", 18); // calling the other constructor
    }
    Student(String name, int age) {
        this.name = name;
        this.age = age;
    }
    void display() {
        System.out.println(name + ", " + age);
    }
}

Example 3: Passing current object using this

Sometimes you might want to pass the current object to another method.

public class Student {
    String name;
    Student(String name) {
        this.name = name;
    }
    void print(Student s) {
        System.out.println("Student name is: " + s.name);
    }
    void show() {
        print(this); // passing current object
    }
}

Summary