equal & hashCode

gistfile1.java

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

import android.app.Activity;
import android.os.Bundle;
import android.util.Log;

public class ListTest extends Activity {
    public static class ModelUnsafe {
        String id;
        public ModelUnsafe(String id) {
            this.id = id;
        }
        @Override
        public String toString() {
            return "[model : " + id + "]";
        }
    }

    public static class ModelSafe extends ModelUnsafe {
        public ModelSafe(String id) {
            super(id);
        }
    
        @Override
        public boolean equals(Object other) {
            if (!(other instanceof ModelSafe)) return false;
            ModelSafe otherModel = (ModelSafe) other;
            
            return id.equals(otherModel.id);
        }
        
        @Override
        public int hashCode() {
            return id.hashCode();
        }
    }

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        ModelUnsafe[] modelsA = new ModelUnsafe[]{
            new ModelUnsafe("A"),
            new ModelUnsafe("B"),
            new ModelUnsafe("C"),
            new ModelUnsafe("D")
        };
        ModelUnsafe[] modelsB = new ModelUnsafe[]{
            new ModelUnsafe("A"),
            new ModelUnsafe("C"),
            new ModelUnsafe("D"),
            new ModelUnsafe("E")
        };
        
        List<ModelUnsafe> modelsListA = Arrays.asList(modelsA);
        List<ModelUnsafe> modelsListB = Arrays.asList(modelsB);
        
        log("calc diff Model");
        calcDiff(modelsListA, modelsListB);
        
        
        ModelSafe[] modelSafesA = new ModelSafe[]{
            new ModelSafe("A"),
            new ModelSafe("B"),
            new ModelSafe("C"),
            new ModelSafe("D")
        };
        ModelSafe[] modelSafesB = new ModelSafe[]{
            new ModelSafe("A"),
            new ModelSafe("C"),
            new ModelSafe("D"),
            new ModelSafe("E")
        };
        List<ModelSafe> modelSafesListA = Arrays.asList(modelSafesA);
        List<ModelSafe> modelSafesListB = Arrays.asList(modelSafesB);
        log("calc diff ModelSafe");
        calcDiff(modelSafesListA, modelSafesListB);
    }
    
    <E> void calcDiff(List<E> a, List<E> b) {
        List<E> intersection = new ArrayList<E>(a);
        List<E> removed = new ArrayList<E>(b);
        List<E> added = new ArrayList<E>(a);
        intersection.retainAll(removed);
        added.removeAll(intersection);
        removed.removeAll(intersection);
        
        log("added : " + added.size() + " " + added);
        log("removed : " + removed.size() + " " + removed);
        log("intersection : " + intersection.size() + " " + intersection);
    }
    
    void log(String msg) {
        Log.d("test", msg);
    }
}