this keyword

class HelloWorld {
 
    public static void main(String[] args) {
        MyClass obj = new MyClass("Hello, Ashish...");
        obj.display(); // output : Hello, Ashish...
    }
}
 
class MyClass {
    String message; //instance variable
 
    HelloWorld(String message) {
        this.message = message; // here 'this' refers to current object's variable
    }
 
    void display() {
        System.out.println(this.message); // here 'this' refers to current object
    }
}

class HelloWorld {
 
    public static void main(String[] args) {
        MyClass obj = new MyClass();
        obj.display();
        //output :
        // Local Variable: Hello from method!
        //Instance Variable: Hello from class!
    }
}
 
class MyClass {
    String message = "Instance Variable: Hello from class!"; // instance variable
 
    void display() {
        String message = "Local Variable: Hello from method!"; // local variable
 
        System.out.println(message);       // refers to local variable
        System.out.println(this.message);  // refers to instance variable
 
        //So here same variable name is used for both local and instance variables, 'this' helps to distinguish them.
    }
}

class HelloWorld {
 
    public static void main(String[] args) {
        MyClass obj = new MyClass(); // Creating object will call the no-argument constructor first
    }
}
 
class MyClass {
 
    // Constructor 1 (no-argument constructor)
    MyClass() {
        // 'this' keyword must be the first statement in the constructor
        this("Hello from parameterized constructor", 100); // this() is used to call constructor-2 of the same class
        System.out.println("No-arg constructor called");
    }
 
    // Constructor 2 (parameterized constructor)
    MyClass(String message, int number) {
        System.out.println("Parameterized constructor called");
    }
}

class HelloWorld {
 
    public static void main(String[] args) {
        MyClass obj = new MyClass();
        obj.show(); //output : Instance method called
    }
}
 
class MyClass {
 
    void display() {
        // instance method
        System.out.println("Instance method called");
    }
 
    void show() {
        // this.display() calls the instance method of current object
        this.display();
    }
}

class HelloWorld {
 
    public static void main(String[] args) {
        show(); 
    }
 
    static void show() {
        // this cannot be used here because show() method is static
        System.out.println(this); // ❌ Compilation error - non-static variable this cannot be referenced from a static context
    } 
}

class HelloWorld {
 
    public static void main(String[] args) {
        MyClass obj = new MyClass();
    }
}
 
class MyClass {
 
    MyClass() {
        // this() must be the first statement in constructor
        this(10);  
 
        System.out.println("No-argument constructor");
    }
 
    MyClass(int x) {
        System.out.println("Parameterized constructor: " + x);
    }
}