this keyword in java

1. this keyword is used to hold address of current instance.

public class Test {

void showCurrentAddress() {
System.out.println(this);
}

public static void main(String[] args) {

Test t1=new Test();
t1.showCurrentAddress();
System.out.println(t1);

Test t2=new Test();
t2.showCurrentAddress();
System.out.println(t2);

}
}

Output is :

Test@5e265ba4
Test@5e265ba4
Test@36aa7bc2
Test@36aa7bc2

2. this keyword is ude to remove confliction between local variable and instance variable.

public class Test {
String name = "Deep Singh";

void showCurrentAddress(String name) {
System.out.println(name);
System.out.println(this.name);
}

public static void main(String[] args) {

Test t1 = new Test();
t1.showCurrentAddress("nikku");

}
}

Output is :

 nikku
 Deep Singh

3. this keyword is used to achieve method chaining by returning this keyword.

public class Test {
Test a() {
System.out.println("a");
return this;
}

Test b() {
System.out.println("b");
return this;
}

Test c() {
System.out.println("c");
return this;
}

public static void main(String[] args) {

new Test().a().b().c();

}
}

Output is :

 a
 b
 c

4. this keyword is used to pass as an argument.

class Friend {

void access(Test t) {
System.out.println(t.roll);
System.out.println(t.name);
}

}

public class Test {
String name;
int roll;

void share() {
new Friend().access(this);
}

public static void main(String[] args) {

Test t = new Test();
t.name = "Deep Singh";
t.roll = 123;

t.share();

}
}

Output is :

 123
 Deep Singh

Note: this keyword can never used inside static context.

this() Constructor in Java

this() is used to call current class constructors or local constructors chaining.

public class Testing {

public Testing() {
this(10);
System.out.println("default constructor");
}

public Testing(int i) {
this("hello");
System.out.println("int constructor");
}

public Testing(String name) {
System.out.println("string constructor");
}

public static void main(String[] args) {
new Testing();
}
}

Output is :

string constructor
int constructor
default constructor

Note : this() constructor must be used inside a constructor and that must be the first statement.