如何检查两个对象在Java中是否具有相同的值？

Question

I have two objects of the same class. The class is containing so many other objects with different types like List<>, ...

What is the best way to determine if this two have the same values? I'm trying to use hashcode function but it doesn't seem to work for me.

public class MyClass{
   List<OtherClass> myList;
   String foo;
   SubClass mySubClass;

   public MyClass(values...){ ... }
   ...
}

MyClass obj1 = new MyClass(values...);
MyClass obj2 = new MyClass(values...); // same values with obj1

if(obj1.hashcode() == obj2.hashcode()){
    System.out.println("This is what I want");
}else{
    System.out.println("This is what happens");
}

Answer 1

You need to override the equals() and hashcode() methods of MyClass.

Your ide can probably do it for you.

What you want is a deep compare. The equals method should go into each list and iterate, and compare.

hashcode should use the hashcode of each element to to generate a hashcode.

Answer 2

Please override the equals method to check for equality. Do not use the hashcode for equality checking.

Please check the java documentation on equals/hashcode, as it is probably too verbose for this post to put the diff. between equals/hashcode and its uses.

In order to compare two Lists, you could simply use the list.equals method... no need to iterate the lists for Ex (Please see java.util.List documentation for equals) ;

// Sample Code...
public class MyClass {
    List<OtherClass> myList;

    public boolean equals(Object o) {
       if (o instanceof List) {
           myList.equals((List) o) ;
       }
       return false;
    }
}

Hope this helps...