package other;
import java.util.Scanner;
public class MyStack {
Object[] oj = new Object[10];
static MyStack ms = new MyStack();
public void method1() {
System.out.println("请选择出栈或入栈，出栈请输入0，入栈请输入1");
Scanner s1 = new Scanner(System.in);
int i = s1.nextInt();
if(i==0) { //出栈
ms.pop();
}else if(i==1) { //入栈
System.out.println("请输入要入栈的元素");
Scanner sn = new Scanner(System.in);
Object ot = sn.next();
ms.push(ot);
}else {
System.out.println("输入有错误请重新输入");
ms.method1();
}
}
public static void main(String[] args) { //主方法
ms.method1();
}
//入栈方法
public void push(Object o) {
for(int i = 0;i<oj.length;i++) {
if(oj[i].equals(null)) {
o = oj[i];
break;
}else if(oj[oj.length-1] != null) {
System.out.println("栈已满，请先出栈");
break;
}
}
}
//出栈方法
public void pop() {
for(int i = oj.length;i>=0;i--) {
if(oj[0] == null) {
System.out.println("栈内无元素，无法出栈");
ms.method1();
}else if(oj[i] != null) {
oj[i] = null;
for(int j = 0;j<oj.length;j++) {
System.out.print("当前栈内元素有:");
System.out.print(oj[j]+" ");
}
break;
}
}
}
}
下面是异常信息
请选择出栈或入栈，出栈请输入0，入栈请输入1
5
输入有错误请重新输入
请选择出栈或入栈，出栈请输入0，入栈请输入1
0
栈内无元素，无法出栈
请选择出栈或入栈，出栈请输入0，入栈请输入1
1
请输入要入栈的元素
1
Exception in thread "main" java.lang.NullPointerException: Cannot invoke "Object.equals(Object)" because "this.oj[i]" is null
at other.MyStack.push(MyStack.java:45)
at other.MyStack.method1(MyStack.java:24)
at other.MyStack.pop(MyStack.java:59)
at other.MyStack.method1(MyStack.java:17)
at other.MyStack.method1(MyStack.java:28)
at other.MyStack.main(MyStack.java:37)
Object 判空 oj[i] == null