Uses of java this keyword

Java this keyword has several uses.this can be used to refer to a current object. Uses 1.Can be used to refer to current va...

Java this keyword has several uses.this can be used to refer to a current object.

Uses

1.Can be used to refer to current variable.
2.can be used to call current class method.
3.Can invoke current class constructor.
4.Can passed in argument method call.
5. Can be passed as argument when calling constructor.
6.Can be used to return current class instance method.

Look at below image that summarizes this keyword uses.

1.Using this to refer to current class variable
Example without this keyword.

/**
 *
 * @author Eric
 */
public class Students {
    
  int id;
String name;
float balance;
 Students(int id,String name,float balance)
{
id=id;
name=name;
balance=balance;
}
   void show()
   {
   System.out.println("ID Number is" +id);
    System.out.println("Name is" +name);
     System.out.println("Balance is" +balance);
   } 
    
   public static void main(String [] args)
   {
   Students s=new Students(123,"Eric mutua",12300f);
    Students s2=new Students(123,"Eric mutua",12300f);
    s.show();
    s2.show();
   }
}

Output:

Same Example with this keyword.

public class Students {
    
  int id;
String name;
float balance;
 Students(int id,String name,float balance)
{
this.id=id;
this.name=name;
this.balance=balance;
}
   void show()
   {
   System.out.println("ID Number is" +id);
    System.out.println("Name is" +name);
     System.out.println("Balance is" +balance);
   } 
    
   public static void main(String [] args)
   {
   Students s=new Students(123,"Eric mutua",12300f);
    Students s2=new Students(124,"Ken",12311f);
    s.show();
    s2.show();
   }
}

Output

Problem where this keyword is not required.

public class Students {
    
  int id;
String name;
float balance;
 Students(int idno,String n,float bal)
{
id=idno;
name=n;
balance=bal;
}
   void show()
   {
   System.out.println("ID Number is" +id);
    System.out.println("Name is" +name);
     System.out.println("Balance is" +balance);
   } 
    
   public static void main(String [] args)
   {
   Students s=new Students(123,"Eric mutua",12300f);
    Students s2=new Students(124,"Ken",12311f);
    s.show();
    s2.show();
   }
}

2.Invoking current class method using this keyword.

public class Students {
    
  int id;
String name;
float balance;
 Students(int idno,String n,float bal)
{
id=idno;
name=n;
balance=bal;
}
   void show()
   {
   System.out.println("ID Number is" +id);
    System.out.println("Name is" +name);
     System.out.println("Balance is" +balance);
   } 
   void call()
   {
       //this method calls method show using this keyword
   this.show();
   }
    
   public static void main(String [] args)
   {
   Students s=new Students(123,"Eric mutua",12300f);
    Students s2=new Students(124,"Ken",12311f);
   s.call();;
   s2.call();
   }
}

3.Invoking current class constructor

Calling default constructor from parameterized constructor:

public class Student {
    Student()
    {
    
    System.out.println("Hello Student");
    }
    Student(int id)
    {
        this();
    System.out.println("Id" +id);
    }
}
    class Test
    {
   public static void main(String args[]){  
    Student s=new Student(124);
    }
    
    }
    

Output:
run:
Hello Student
Id124

BUILD SUCCESSFUL (total time: 0 seconds)

Calling parameterized constructor from default constructor:

public class Student {
    Student()
    {
         this(45);
    
    System.out.println("Hello Student");
    }
    Student(int id)
    {
       
    System.out.println("Id" +id);
    }
}
    class Test
    {
   public static void main(String args[]){  
    Student s=new Student();
    }
    
    }
    

Output
run:
Id45
Hello Student

BUILD SUCCESSFUL (total time: 0 seconds)

4.using this keyword to pass an argument to a method

public class Student {
    void show(Student s)
    {
          System.out.println("method is invoked");  
        
    }
    void invoke()
    {
    show(this);
    }
    
   public static void main(String args[]){  
    Student s=new Student();
    s.invoke();
    
    }
}
    

Output

method is invoked

BUILD SUCCESSFUL (total time: 0 seconds)

5.Using this keyword to pass an argument to a constructor.

class BB{  
  AA4 obj;  
  BB(AA4 obj){  
    this.obj=obj;  
  }  
  void display(){  
    System.out.println(obj.data);//using data member of AA4 class  
  }  
}  
  
class AA4{  
  int data=10;  
  AA4(){  
   BB b=new BB(this);  
   b.display();  
  }  
  public static void main(String args[]){  
   AA4 a=new AA4();  
  }  
}

6.using this keyword to return current class interface

class AA{  
AA getAA(){  
return this;  
}  
void msg(){System.out.println("Hello java");}  
}  
class Test1{  
public static void main(String args[]){  
new AA().getAA().msg();  
}  
}

See also:

The use of Java static keyword