How to compare Objects values which is inside two different list in Java?

Question

I have two Lists, say listA and listA1, listA contains object of class A type and listA1 also contains object of type class A.But listA added class A objects by java code and listA1 adds class A objects by converting JSON String to Class A.

Now I need to compare listA and listA1. If listA contains any objects which also are in listA1 I need to remove that object and return back listA with all the objects which are not in listA1.

How can I achieve this in Java?

@zander I used contains() method which is working fine when objects are same its not comparing values.. — Subodh Joshi, Oct 11 '12 at 04:57
First of all Class A must have a "valid" equals implementation, then we can use [List.removeAll](http://docs.oracle.com/javase/1.4.2/docs/api/java/util/List.html#removeAll%28java.util.Collection%29) — white, Oct 11 '12 at 04:58
Implement a custom(your own) equals method for class A and use this method to compare and remove the objects using the method suggested by @white — krishnang, Oct 11 '12 at 04:59
Read http://stackoverflow.com/questions/27581/overriding-equals-and-hashcode-in-java, implement equals and hashCode — Jayan, Oct 11 '12 at 05:00

Yogendra Singh · Accepted Answer · 2012-10-11T05:36:03.320

1

Please implement(override) equals method as below on your class A. Once done, contains method should help.

  public boolean equals(A a){
       boolean bEqual = false;
       if(this.value1!= null && a.value1!= null && 
          this.value1.eqauls(a.value1)
          ........
          ........
        ) {
          bEqual = true;              
        }
        return bEqual;
   }

EDIT:

Iterate elements of listA1. If they are present in listA, remove them.

   for(A a: listA1){
     if(listA.contains(a)){
        listA.remove(a);
     }
   }

edited Oct 11 '12 at 05:36

answered Oct 11 '12 at 04:58

Yogendra Singh

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listA contains 15 element(Class A's object) and listA1 contains 5 elements(Class A's object) now i have to compare values of objects(listA and listA1) and remove all the objects from listA and which are also present in listA1.Thanks – Subodh Joshi Oct 11 '12 at 05:18
Thanks Yogendra i am doing same for (A : listA) { if (listA.contains(A)) { listA.remove(value); } } but that not working may be the addres of objects are diffrent because contains not checking values its checking address of object .its my thinking – Subodh Joshi Oct 11 '12 at 05:27
If it works for you, please don't forget to accept to close this question thread. – Yogendra Singh Oct 11 '12 at 05:28
Did you implement the equals method (comparing field values) in your class `A`? – Yogendra Singh Oct 11 '12 at 05:35
Please share you class `A` attributes with their data type. I will help you implement the `equals` method. – Yogendra Singh Oct 11 '12 at 05:53
Thanks i used your solution and i posted what exact code i did . – Subodh Joshi Oct 11 '12 at 06:05

score 0 · Answer 2 · answered Oct 11 '12 at 05:01

Apache's commons.collections library has a CollectionUtils class that provides easy-to-use methods for Collection manipulation/checking, such as intersection, difference, and union.

The org.apache.commons.collections.CollectionUtils API docs are here.

I think, You can use intersaction methos for that

score 0 · Answer 3 · answered Oct 11 '12 at 05:03

0

You need to override the .equals(Oject) and the .hashCode() methods in your class.
hashCode isn't needed for the List, but when you override equals the contract says you have to override hashCode

answered Oct 11 '12 at 05:03

Sumit Singh

24,095
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score 0 · Answer 4 · answered Oct 11 '12 at 05:25

0

If you are planning to compare two objects, then see the comparing objects

also, How it works equals

answered Oct 11 '12 at 05:25

subodh

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score 0 · Answer 5 · answered Oct 11 '12 at 06:05

What exact thing i did to resolve the issue.....

 public static class A  {


        String  headerName;

        public String getHeaderName() {
            return headerName;
        }
        public void setListBoxHeaderName(String headerName) {
            this.headerName= headerName;
        }
        public A(String headerName) {
            super();

            this.headerName = headerName;
        }


        public boolean equals(A rData) {
            boolean bEqual = false;
            if (this.getHeaderName() != null && rData.getHeaderName() != null
                    && this.getHeaderName().equals(rData.getHeaderName())) {
                bEqual = true;
            }
            return bEqual;
        }

    }

And for comparing two list the code is as follows...

for (A value1 : listA1) {
            for (A value2: listA) {
                if (value2.equals(value1 )) {
                 listA.remove(value2);
                    break;
                }
            }
        }

This is what the exact solution i used Thanks

How to compare Objects values which is inside two different list in Java?

5 Answers5