JavaSE---java.util---ArrayList

public boolean contains(Object o) {
        return indexOf(o) >= 0;
    }


public int indexOf(Object o) {
        if (o == null) {
            for (int i = 0; i < size; i++)
                if (elementData[i]==null)
                    return i;
        } else {
            for (int i = 0; i < size; i++)
                if (o.equals(elementData[i]))
                    return i;
        }
        return -1;
    }

public int indexOf(Object o) {
        if (o == null) {
            for (int i = 0; i < size; i++)
                if (elementData[i]==null)
                    return i;
        } else {
            for (int i = 0; i < size; i++)
                if (o.equals(elementData[i]))
                    return i;
        }
        return -1;
    }

public E get(int index) {
        rangeCheck(index);

        return elementData(index);
    }

@SuppressWarnings("unchecked")
    E elementData(int index) {
        return (E) elementData[index];
    }