java - 如何从数组末尾删除一个元素并将其插入到前面

Question

我正在使用 arraylist 工具。我想编写一个获取最后一个元素并将其插入到前面的方法。到目前为止，我得到了最后一个元素并将其插入前面，然后将所有内容都移了过来。但是，我似乎无法删除前面插入的最后一个元素。例如:(1,2,5)到(5,1,2)但我得到了(5,1,2,5)。我在我的 replaceArray() 方法中遗漏了一些东西，但我真的不知道是什么。感谢您的帮助。

类的构造函数:

public KWArrayList() {
    capacity = INITIAL_CAPACITY;
    theData = (E[]) new Object[capacity];
}

public void replaceArray(int index, E anElement) {
    for (int i = size; i > index; i--){
        theData[i] = theData[i - 1];
    }

    theData[index] = anEntry;

    size--;

    for (int i = 0; i < theData.length; i++){
        System.out.println(theData[i]);
    }
}

Answer 1

我会使用这种旋转数组的简单方法(我认为该方法应该称为 rotate 而不是 replaceAll，因为它实际上是将数组旋转一个位置) .

这是方法 rotate():

@SuppressWarnings("unchecked")
public void rotate() {
    Object[] temp = new Object[theData.length];
    //copy each element, except the first, from theData into temp by shifting one position off to the right
    for (int i = temp.length - 1; i > 0; i--) {
        temp[i] = theData[i - 1];
    }
    //move the last element into the first position
    temp[0] = theData[theData.length - 1];
    //update theData
    theData = (T[]) temp;
}

完整的可测试示例

public class MyArrayList<T> {
    int INITIAL_CAPACITY = 10;
    int capacity;
    T[] theData;

    @SuppressWarnings("unchecked")
    public MyArrayList() {
        capacity = INITIAL_CAPACITY;
        theData = (T[]) new Object[capacity];
    }

    @SuppressWarnings("unchecked")
    public MyArrayList(int capacity) {
        this.capacity = capacity;
        theData = (T[]) new Object[this.capacity];
    }

    @SuppressWarnings("unchecked")
    public void rotate() {
        Object[] temp = new Object[theData.length];
        //copy each element, except the first, from theData into temp by shifting one position off to the right
        // to the right
        for (int i = temp.length - 1; i > 0; i--) {
            temp[i] = theData[i - 1];
        }
        // move the last element into the first position
        temp[0] = theData[theData.length - 1];
        // update theData
        theData = (T[]) temp;
    }

    /**
     * For testing purposes only. It doesn't handle out of bounds values of
     * index.
     */
    private void insert(T t, int index) {
        theData[index] = t;
    }

    public void print() {
        for (T t : theData) {
            System.out.print(t + ", ");
        }
        System.out.println();
    }

    @SafeVarargs
    public static <E> MyArrayList<E> of(E... elements) {
        MyArrayList<E> m = new MyArrayList<>(elements.length);
        for (int i = 0; i < elements.length; i++) {
            m.insert(elements[i], i);
        }
        return m;
    }
}

测试rotate()方法:

public class TestMyArrayList {
    public static void main(String[] args) {
        MyArrayList<Integer> m = MyArrayList.of(1, 2, 3, 4, 5);
        m.print();
        m.rotate();
        m.print();
    }
}

它会打印出:

1, 2, 3, 4, 5, 
5, 1, 2, 3, 4,