用Java检查类的天气对象是否分配了类实例的方法是什么？

Question

I've put just small snippet of large code to explain my question:

class A 
{
    B b= new B();
    B z; 
    void xyz(){
        if(// condition to check z is not assigned instance of class B){
        z=b;
        }
        else{
        z= new B();
        }
    }
}

class B{
//variables and methods
}

I want an Expression in if block of xyz() to check weather object z have assigned an instance of B or not where I've made comment in if block's bracket. or in other way.

what is a way to check weather any java object have instance of their class or not?

Answer 1

Using instanceof you can check this

Try this:

        B b= new B();
        B z = null; 
        if( z instanceof B){
           z=b;
           System.out.println("yes");
        } else{
           z = new B();
           System.out.println("no");
        }