this Keyword In Java

All java developer aware role of 'this'. 'this' is a reference to the current object in constructor and instance methods.

In java we use 'this' in different place are:

1. Using 'this field' inside constructor/non-static method.

2. Using 'this field' inside static method.

3. Using this() method inside constructor

4. Using this() method inside static/non-static methods.

5. Recursive constructor invocation using this().

S.No.	Place of 'this'	Description	When executes	Where Not Include	Sample Code
1	Using 'this field' inside constructor/non-static method	'this' act as the reference to the current object, So using 'this' we can access the class instance variable and methods(static/no-static). Most of the case we use in POJO class setter & getter method.	We can use to refer the current object instance variable inside the constructor/non-static methods.	Its should be used anywhere in inside constructor/non-static method.	package thispck; public class SampleThis { int intvalue; public SampleThis(int intvalue) { this.intvalue=intvalue; } public static void main(String arg[]) { SampleThis sampleThis=new SampleThis(10); System.out.println("Int Value::"+sampleThis.intvalue); } } Output: Int Value::10
2	Using 'this field' inside static method.	Not possible to use this.	-	Compile time error. Error: cannot use this in a static context.	-
3	Using 'this() method' inside constructor	This() method used for calling the default constructor and parameter constructor in a class.	While object creation using new keyword.	'this()' declaration should be first statement in constructor. Otherwise compile time Error: Constructor call must be first statement in constructor	package thispck; public class SampleThis { int intvalue; public SampleThis(int intvalue) { this.intvalue=intvalue; } public SampleThis() { this(0); } public static void main(String arg[]) { SampleThis sampleThis=new SampleThis(10); System.out.println("Int Value::"+sampleThis.intvalue); } } output: Int Value::10
4	Using this() method inside static/non-static methods.	Compile time error	-	Error: Constructor call must be the first statement in a constructor	-
5	Recursive constructor invocation using this()	Compile time error	-	Compile time error. public SampleThis(int intvalue) { this(); this.intvalue=intvalue; } public SampleThis() { this(0); }	package thispck; public class SampleThis { int intvalue; public SampleThis(int intvalue) { this(); this.intvalue=intvalue; } public SampleThis() { this(0); } public static void main(String arg[]) { SampleThis sampleThis=new SampleThis(10); System.out.println("Int Value::"+sampleThis.intvalue); } }