Question

Why does the code throw null pointer Exception and what is the meaning of using ‘this’. I am beginner, value any help.

// class Foobar
private Foo f;
void get(){
    this.getFoo().handle();
}  
public Foolish getFoo(){
    return this.f;
}
void handle(){
    System.out.println("handle of the intrf");
}

// please note that

public interface Foolish {
    void handle();
}

//main
public static void main(String[] args) {
    new Foobar().get();

Answer 1

The reason that you get an exception is that the member f of type Foo is not initialized to, say, new Foo() somewhere in the constructor or in the declaration.

The reference to this in this context means “the object itself”; it is entirely not necessary in your code, because there is nothing to disambiguate.