TreeMap实现中的Put方法

Question

I'm implementing a TreeMap class called MyTreeMap, and the put method is giving me some trouble. During testing, instead of updating the value of a key that is already there, it just seems to clear the node entirely. Here is the code:

public class MyTreeMap<K extends Comparable<? super K>,V> extends AbstractMap<K,V>  {

K key;
V value;
int height;
MyTreeMap<K,V> left,right;
int size;

public V put(K key, V value) {

    if(this.isEmpty()) {
        this.key = key;
        this.value = value;

        this.size++;
        setHeight();

        return null;
    }

    else if(this.key.compareTo(key) == 0) {
        V temp = this.value;
        this.value = value;
        return temp;
    }

    else if(this.key.compareTo(key) > 0) {
        if(this.left == null) {
            this.left = new MyTreeMap<K,V>(key,value,null,null);
            this.size++;
            if(left.height > right.height + 1 || right.height > left.height + 1)
                restructure(this);
            setHeight();
            return null;
        }
        else
            return this.left.put(key, value);
    }
    else {
        if(this.right == null) {
        this.right = new MyTreeMap<K,V>(key,value,null,null);
        this.size++;
        if(left.height > right.height + 1 || right.height > left.height + 1)
            restructure(this);
        setHeight();    
        return null;
        }
        else
            return this.right.put(key, value);
    }
}

Here is the test, the first assertEquals passed, the second one did not, the failure trace is shown at a comment in that line

@Test
public void putTest2() {
    TreeMap<String,LinkedList<Integer>> actual = new TreeMap<String,LinkedList<Integer>>();
    MyTreeMap<String,LinkedList<Integer>> test = new MyTreeMap<String,LinkedList<Integer>>();

    LinkedList<Integer> actualList = new LinkedList<Integer>();
    actualList.add(0);
    actualList.add(4);

    LinkedList<Integer> testList = new LinkedList<Integer>();
    testList.add(0);
    testList.add(4);

    actual.put("hello", actualList);
    test.put("hello", actualList);

    assertEquals(actual, test); //this part passes, indicating that it adds new keys correctly

    LinkedList<Integer> tempList;

    tempList = actual.get("hello");

    tempList.add(6);

    actual.put("hello", tempList);
    test.put("hello", tempList);

    assertEquals(actual, test); //this part fails, fail trace: expected:<{hello=[0,4,6,6]}> but was <[]>
}

}

If you could give me any help on solving this bug, that would be helpful. Thanks.

Answer 1

In this case, assertEquals(a, b) tests if the two Map parameters are the same object , not that they contain the same values .

Neither your class nor TreeMap implement equals() so the default implementation from the Object class is used, which simply returns a == b .

Have a look at the Hamcrest library for meaningfully comparing collections by value.