how to make a set of array in java?

Question

Since the equals function in array only check the instance, it doesn\'t work well with Set. Hence, I wonder how to make a set of arrays in java?

One possible way cou

Answer 1

Since the ArrayList class already wraps an array, you can extend it and override the equals and hashCode methods. Here is a sample:

public MyArrayList extends ArrayList<MyClass> {

    @Override
    public boolean equals(Object o) {
        if (o instanceof MyArrayList) {
            //place your comparison logic here
            return true;
        }
        return false;
    }

    @Override
    public int hashCode() {
        //just a sample, you can place your own code
        return super.hashCode();
    }
}

UPDATE:

You can even override it for a generic use, just changing the code to:

public MyArrayList<T> extends ArrayList<T> {
    //overrides the methods you need
    @Override
    public boolean equals(Object o) {
        if (o instanceof MyArrayList) {
            //place your comparison logic here
            return true;
        }
        return false;
    }
}

Answer 2

You could create a wrapper class for your array and override hashcode and equals accordingly. For example:

public class MyArrayContainer {
int[] myArray = new int[100];
@Override
public boolean equals(Object other) {
     if (null!= other && other instanceof MyArrayContainer){
     MyArrayContainer o = (MyArrayContainer) other;
     final int myLength = myArray.length; 
     if (o.myArray.length != myLength){
         return false;
     }
     for (int i = 0; i < myLength; i++){
         if (myArray[i] != o.myArray[i]){
              return false;
         }
     }
     return true;
     }
     return false;
}

@Override
public int hashCode() {
     return myArray.length;
}   
}

Answer 3

A class that extends Set and override the equals method could do it.

Answer 4

If you make your Set be an instance of TreeSet, you can specify a custom Comparator which will be used for all comparisons (even equality).

Answer 5

Don't use raw Arrays unless you absolutely have to because of some legacy API that requires an Array.

Always try and use a type safe ArrayList<T> instead and you won't have these kind of issues.