将原始对象与堆栈/队列进行比较-覆盖equals（）方法

Question

I've created a class which can be inherited to create both a Stack and a Queue using LinkedLists, I've passed all the JUnit tests except the equals one, I still have no idea why it doesn't work.

@Override public boolean equals(Object o) {

    if( o == null) return false;
    if(o == this) return true;


    if(!(o instanceof PushPop)) return false;
    PushPop test1= this;
    PushPop test = (PushPop)o;
    while(!test.isEmpty() && !test1.isEmpty()){
        if(test1.pop() != test.pop()) return false;
    }
    return true;
}

The test sends out an assertion error whenever it's comparing the values, specifically whenever a stack/queue has an extra value than the second one.

Answer 1

OK, I have located your problem:

In your test, you do the following [taken from comment]

stack.push(i);
Assert.assertFalse(stack.equals(stack2));
stack2.push(i);
Assert.assertTrue(stack.equals(stack2));

This seems reasonable. However, equals clears both stacks so when you push i onto stack2 , it is no longer equal to the now-empty stack .

Hence your error.

The solution: Don't Modify Your Object In An equals Method.

I'd suggest cloning or comparing whatever your underlying data structure is (eg, if you're using Nodes, having Node implement equals ).