Java classes reference each other

Question

I have two java class files. Each of them has methods the other one uses.

public class class1{
    class2 c2 = new class2(); 
    m1(){
        c2.ma(); 
            


        

Answer 1

What actually happens is that you create an instance of Class1 in the constructor,

• which creates an instance of Class2 in the constructor,
  • which creates an instance of Class1 in the constructor,
    • which creates an instance of Class2 in the constructor,
      • et cetera.

Your constructors are recursingly creating instances, causing the call stack to flood, resulting in a StackOverflowError.

I assume you want an instance of Class1 to hold a reference to an instance of Class2 and vice versa?

In that case, you can just do this:

public class Class1 {

    private Class2 c2;

    public Class1() {
        this.c2 = new Class2(this);
    }
}

public class Class2 {

    private Class1 c1;

    public Class2(Class1 class1) {
        this.c1 = class1;
    }
}

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Cyclic aggregations like this are often a sign of a bad design; but there are situations where it is perfectly valid, or at least reflects reality.