The “this keyword” in Java refer to the the current object (current instance). All your instance variables may be referred as 'this.variableName' even though it is implicit in most cases. 

The “this keyword”  is mostly useful in below cases:

1. Refer to instance variables of a class when a local variable has precedence over it.

   • A local variable with same name as the instance variable will take precedence over the instance variable in the local variable’s scope. We can use this keyword in such cases to refer to the instance variable. A major use of this approach comes in the setter methods.

2. We can call one constructor from another constructor using this().

   • Similar to methods, we can overload constructors i.e. we can have more than one constructor with same name and but different parameter set. Note that constructor names for a class are always same as it is the class name itself.

   • Java won’t allow us to create an infinite loop by calling one constructor from another and then the other calling it back. Compilation will fail because of “Recursive constructor invocation”.

   • Similarly you may call a super class constructor using super() keyword (we will discuss about super later.)

3. To refer to the current object and pass it to a method or return it from a method

   • Someone might want to get the reference to the current object.

   • You may also register yourself (current object) as a listener in some callback register.

Important Note

1. Since this object represent the current object in question (whichever object user created using new), it cannot be used from a static context. 

   1. However, we can refer to a static variable using a this pointer (from an instance context.)

Examples

Example: Refering to instance variables of a class when a local variable has precedence over it.

class MyClass{

 int myVar=5;

 public void setMyVar(int myVar)

 {

   this.myVar = myVar;

 }

}

Example: Calling one constructor from another constructor using this().

 class MyClass{

 int myVar=5;

 public void setMyVar(int myVar)

 {

   this.myVar = myVar;

 }

}

Example 3: Refering to the current object and pass it to a method or return it from a method.

We can invoke a method with signature myMethod(MyClass c) from MyClass as:

myMethod(this);

We can return the current object from a method with return type MyClass from MyClass as:

public MyClass getInstance()

{

...

return this;

}