drop-out栈

1、drop-out栈能够用来做什么？

　　在许多提供编辑功能的软件，如word、ps、画图，都会提供“撤销”和“恢复”功能，使用drop-out能够实现这些功能。

2、drop-out栈特性

　　drop-out栈是一种特殊的栈，具有如下特征：

　　1、栈的大小固定

　　2、如果在栈满的情况下希望往栈中压入一个数据，栈底的数据会被清除以腾出空间容纳要新的数据。

3、drop-out栈实现

　　在此提供一种drop-out栈的实现方法：循环队列

package learnspring.learnspring.normalJava;

import java.awt.datatransfer.StringSelection;

/**
 * @author 肖政宇
 * @date 2019-09-28 21:21
 * 说明：drop-out栈具有这样的特性：栈满以后，如果试图向栈中压入数据，
 * 栈底的数据会自动被弹出。
 */
public class DropOutStack {
    /**
     * size - 栈大小
     * stack - 栈
     * top - 栈顶（当前能够插入数据的位置）
     * bottom - 栈底
     * total - 栈内数据总数
     */
    private final int size;
    private Object[] stack;
    private int top;
    private int bottom;
    private int total;

    /**
     * constructor
     *
     * @param stackSize - the size of the stack
     * @throws Exception - wrong size
     */
    public DropOutStack(int stackSize) throws Exception {
        if (stackSize <= 1) {
            throw new Exception("wrong value！" + stackSize);
        }
        this.size = stackSize;
        this.stack = new Object[stackSize];
        this.top = 0;
        this.bottom = 0;
        this.total = 0;
    }

    /**
     * get the size of the stack
     *
     * @return - the size of the stack
     */
    public int size() {
        return size;
    }

    /**
     * push a data into the stack
     *
     * @param object = data that you want to push onto the stack
     * @return - true or false
     */
    public Boolean push(Object object) {
        try {
            stack[top] = object;
            top = (top + 1) % size;
            //stack is full
            if (total == size) {
                //the bottom element have been drop
                bottom = (bottom + 1) % size;
            } else {//stack is not full yet
                total++;
            }
            return true;
        } catch (Exception e) {
            e.printStackTrace();
            return false;
        }
    }

    /**
     * get the data from the top of the stack
     *
     * @return - a data from the top of the stack
     * @throws Exception - the stack is empty
     */
    public Object peek() throws Exception {
        if (total == 0) {
            throw new Exception("the stack is empty!");
        }
        //get the data from the top of the stack
        top = top == 0 ? size - 1 : top - 1;
        return stack[top];
    }

    /**
     * drop a data from the top of the stack
     *
     * @return - a data from the top of the stack
     * @throws Exception - the stack is empty
     */
    public Object pop() throws Exception {

        if (total == 0) {
            throw new Exception("the stack is empty!");
        }
        //get the data from the top of the stack
        top = top == 0 ? size - 1 : top - 1;
        Object object = stack[top];
        //delete the data from the top of the stack
        stack[top] = null;
        //change the number of elements in the stack
        total--;
        return object;
    }

    /**
     * Is the stack empty？
     *
     * @return - true or false
     */
    public Boolean isEmpty() {
        return total == 0;
    }

    @Override
    public String toString() {
        StringBuilder stringStack = new StringBuilder();
        stringStack.append('[');
        for (int i = 0; i < size; i++) {
            if (stack[i] != null) {
                stringStack.append(stack[i]);
            } else {
                stringStack.append("null");
            }
            if (i + 1 < size) {
                stringStack.append(',');
            }
        }
        stringStack.append(']');
        return stringStack.toString();
    }
}