In this tutorial, we will learn the use of 'this' keyword in Java.
In Java, the this keyword is used within a class to refer to the current instance (object) of that class. It’s commonly used in methods or constructors to reference the current object’s properties or to call other constructors within the same class.
class Main {
int instVar;
Main(int instVar) {
this.instVar = instVar;
System.out.println("this reference = " + this);
}
public static void main(String[] args) {
Main obj = new Main(8);
System.out.println("object reference = " + obj);
}
}this reference = Main@23fc625e
object reference = Main@23fc625eIn this example, this refers to the obj instance of Main. Both this and obj share the same memory reference, indicating that this represents the current object.
When instance variables and parameters have the same name, using this helps to avoid ambiguity:
class MyClass {
int age;
MyClass(int age) {
this.age = age; // Uses `this` to differentiate instance variable from parameter
}
}Without this:
class Main {
int age;
Main(int age) {
age = age; // No `this`, so no assignment to the instance variable
}
public static void main(String[] args) {
Main obj = new Main(8);
System.out.println("obj.age = " + obj.age); // Output: obj.age = 0
}
}this is often used in setter methods to differentiate between instance variables and parameters:
class Main {
String name;
void setName(String name) {
this.name = name;
}
String getName() {
return this.name;
}
public static void main(String[] args) {
Main obj = new Main();
obj.setName("Toshiba");
System.out.println("obj.name: " + obj.getName());
}
}obj.name: ToshibaIn constructor overloading, this() can be used to call another constructor within the same class, reducing code duplication:
class Complex {
private int a, b;
// Constructor with two parameters
Complex(int i, int j) {
this.a = i;
this.b = j;
}
// Single parameter constructor calls two-parameter constructor
Complex(int i) {
this(i, i);
}
// No-argument constructor calls single-parameter constructor
Complex() {
this(0);
}
@Override
public String toString() {
return this.a + " + " + this.b + "i";
}
public static void main(String[] args) {
Complex c1 = new Complex(2, 3);
Complex c2 = new Complex(3);
Complex c3 = new Complex();
System.out.println(c1); // Output: 2 + 3i
System.out.println(c2); // Output: 3 + 3i
System.out.println(c3); // Output: 0 + 0i
}
}Here, this() helps to manage multiple constructors, improving readability and reducing code duplication. However, it should be used carefully, as excessive use can slow down the program.
You can use this to pass the current object as an argument to other methods:
class ThisExample {
int x;
int y;
ThisExample(int x, int y) {
this.x = x;
this.y = y;
System.out.println("Before passing this:");
System.out.println("x = " + this.x + ", y = " + this.y);
add(this);
System.out.println("After passing this:");
System.out.println("x = " + this.x + ", y = " + this.y);
}
void add(ThisExample obj) {
obj.x += 2;
obj.y += 2;
}
public static void main(String[] args) {
ThisExample obj = new ThisExample(1, -2);
}
}Before passing this:
x = 1, y = -2
After passing this:
x = 3, y = 0In this example, this allows the add() method to modify the current instance variables directly.
this resolves conflicts when instance variables and parameters share the same name.this is often used in setters to distinguish instance variables.this() can call other constructors within the same class, helping to reduce code redundancy.this allows you to pass the current object as a method argument, enabling modifications on the current instance.