数据结构之基于Java的顺序栈实现

本文的代码来自于《数据结构与算法（JAVA语言版）》，是笔者在网上找到的资料，非正式出刊版物。笔者对代码一些比较难以理解的部分添加了注释和图解，欢迎大家来讨论。

public class StackArray implements Stack {

private final int LEN = 4;  //数组的默认大小
private Object[] elements;  //数据元素数组
private int top;            //栈顶指针

public StackArray() {
        top = -1;
        elements = new Object[LEN];
    }

public int getSize() {
return top+1;
    }//返回堆栈的大小

public boolean isEmpty() {
return top<0;
    }//判断堆栈是否为空

public void push(Object e) {
if (getSize()>=elements.length) expandSpace();
        elements[++top] = e;
    }//数据元素e入栈

private void expandSpace(){
        Object[] a = new Object[elements.length*2];
for (int i=0; i<elements.length; i++)
            a[i] = elements[i];
        elements = a;
    }

public Object pop() throws StackEmptyException {
if (getSize()<1)
throw new StackEmptyException("错误，堆栈为空。");
        Object obj = elements[top];
        elements[top--] = null;
return obj;
    }//栈顶元素出栈

public Object peek() throws StackEmptyException {
if (getSize()<1)
throw new StackEmptyException("错误，堆栈为空。");
return elements[top];
    }//取栈顶元素
}

---

public interface Stack {
//返回堆栈的大小
public int getSize();

//判断堆栈是否为空
public boolean isEmpty();

//数据元素e入栈
public void push(Object e);

//栈顶元素出栈
public Object pop() throws StackEmptyException;

//取栈顶元素
public Object peek() throws StackEmptyException;
}

---

package dsa.exception;

//堆栈为空时出栈或取栈顶元素抛出此异常
public class StackEmptyException extends RuntimeException{

public StackEmptyException(String err) {
super(err);
    }   
}