java初学，Java完全参考手册(第8版) 第132页实例代码报错

package java完全参考手册.类;

class stack {
    int stck[] = new int[4];
    int tos;

    // initialize top-of-stack
    // 初始化top-of-stack
    stack () {
        this.tos = -1;
    }

    // push an item onto the stack 
    // 把项压入堆栈
    void push (int item) {
        if (this.tos == 9) {
            System.out.println("stack is full");
        } else {
            this.stck[++this.tos] = item;
        }
    }

    // pop an item form the stack 
    // 流行一个项目形成堆栈
    int pop () {
        if (this.tos < 0) {
            System.out.println("stack underflow.");
            return 0;
        } else {
            return this.stck[this.tos--];
        }
    }
}

public class textstack {

    public static void main(String[] args) {
        stack mystack1 = new stack();
        stack mystack2 = new stack();

        // push some number onto the stack.
        // 把一些压入堆栈.
        for (int i = 0; i < 10; i++) {
            mystack1.push(i);
        }

        for (int i = 10; i < 20; i++) {
            mystack2.push(i);
        }

        // pop those numbes off the stack.
        // 流行那些麻木的堆栈。
        System.out.print("stack in mystack1: ");
        for (int i = 0; i < 10; i++){
            System.out.println(mystack1.pop()); 
        }
        System.out.print("stack in mystack2: ");
        for (int i = 0; i < 10; i++){
            System.out.println(mystack2.pop()); 
        }
    }
}

如题：一直没找到原因，eclipse也没提示信息！
Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 4
at java完全参考手册.类.stack.push(textstack.java:19)
at java完全参考手册.类.textstack.main(textstack.java:44)
求高手帮我看看！

找到原因了，Array范围，结贴！