arraystack.java~7~

源程序（包括最初的版本

package stack;

/**

 */
import java.util.*;
public class ArrayStack implements Stack {
    //data members
    int top;// the current top of stack
    Object []stack; //element array

    //constructors
    public ArrayStack(int initialCapacity) {
        if(initialCapacity<1)
            throw new IllegalArgumentException
                  ("initialCapacity must be >=1");
        stack=new Object[initialCapacity];
        top=-1;
    }
    public ArrayStack() {
        this(10);
    }

    public boolean empty() {
        return top==-1;
    }
    public Object peek(){
        if(empty())
            throw new EmptyStackException();
        return stack[top];
    }

    // 内部方法，用新长度newLength进行栈空间的扩容
      Object []  ChangeArrayLength(Object [] element, int newLength)
      {
        // 以希望的长度及同样的类型分配数组空间
        Object [] newArray = new Object [newLength];

        // 老空间元素到新空间的拷贝
        for(int i=0;i<element.length;i++)
            newArray[i]=element[i];

        // 返回新空间
        return newArray;
      }

    public void push(Object theElement) {
        if(top==stack.length-1)
            stack=ChangeArrayLength(stack,2*stack.length);
        stack[++top]=theElement;
    }

    public Object pop() {
        if(empty())
            throw new EmptyStackException();
        Object topElement=stack[top];
        stack[top--]=null;
        return topElement;
    }

    /** 到字符串的转换 */
      public String toString()
      {
         StringBuffer s = new StringBuffer("[");

      // 添加元素到字符缓冲区
         for (int i = 0; i <stack.length; i++)
            if (stack[i] == null)
               s.append("null, ");
            else
               s.append(stack[i].toString() + ", ");

         if (stack.length > 0)
            s.delete(s.length() - 2, s.length());  // 去掉最后一个 ","

         s.append("]");

      // 返回创建的字符串 s
         return new String(s);
      }


    //测试方法
    public static void main(String args[]){
        //构造一个栈，初始为十个空间
        ArrayStack element=new ArrayStack();

        //判断栈空
        if(element.empty()==true) {
            System.out.println("the stack is empty");
        }

        //入栈
        element.push(new Integer(1));
        element.push(new Integer(2));
        element.push(new Integer(3));
        System.out.println("the stack is "+element);

        //获得栈顶元素
        System.out.println("the top is "+element.peek());

        //出栈
        System.out.println("the out  is "+element.pop());
        System.out.println("now the top is "+element.peek());
    }
}