闲暇之中随便写一个java的小程序 但是有错误 实在是找不到 抓狂死了 请大家帮忙 很简单的问题：
就是一个最普通的linked list 插入问题
public class linkList{
class list{
int value;
list next;//=null;
}
list head=null;
public void insert (int num){
list newNode=new list();
list runner;
list previouse;
newNode.value=num;
if(head==null){
head=newNode;
newNode.next=null;
}
else
{
previouse=null;
runner=head;
while(runner.value<num&&runner!=null){
previouse=runner;
runner=runner.next;
}
if(previouse==null){
head=newNode;
newNode.next=runner;
}
else if(runner==null){
previouse.next=newNode;
newNode.next=runner;
}
}
}
public void printList(){
list runner=new list();
if(head==null)
System.out.println("This is an empty list!");
else{
runner=head;
while(runner!=null){
System.out.println(runner.value);
runner=runner.next;
}
}
}
}
main function 在另一个文件：
import java.io.*;
public class driver {
public static void main(String[] args){
int number;
linkList myList=new linkList ();
for(int i=0;i<10;i++){
myList.insert(i);
}
myList.printList();
}
}
不知道为什么就是有错， 如果我插入的顺序是 10， 9， 8， 7，。。。。1 就没事
但如果我要是正着插入1，2，3，4，5.。。。10 就会出错 报错说：
Exception in thread "main" java.lang.NullPointerException
at binaryTree.insert(binaryTree.java:30)
at driver.main(driver.java:10)
我就是不知道为什么 大家快告诉我 让我别再抓狂了。。。
------解决方案--------------------
while (runner != null&&runner.value < num){
previouse = runner;
runner = runner.next;
}
其他逻辑没怎么看，别抓狂了。应该就是这个问题。
------解决方案--------------------
------解决方案--------------------
at binaryTree.insert(binaryTree.java:30)
binaryTree.java的30行报空指针
- Java code
class list { int value; list next;// =null;}public class linkList { list head = null; public void insert(int num) { list newNode = new list(); list runner; list previouse; newNode.value = num; if (head == null) { head = newNode; newNode.next = null; } else { previouse = null; runner = head; while (runner != null && runner.value < num) { // 你的写法有点问题，应该先判断是否为null // 在判断value，因为&&是短路操作符，如果runner为null了，就不会判断.value // < num,按照你的写法，如果runner为null则会报空指针 previouse = runner; runner = runner.next; } if (previouse == null) { head = newNode; newNode.next = runner; } else if (runner == null) { previouse.next = newNode; newNode.next = runner; } } } public void printList() { list runner = new list(); if (head == null) System.out.println("This is an empty list!"); else { runner = head; while (runner != null) { System.out.println(runner.value); runner = runner.next; } } } public static void main(String[] args) { int number; linkList myList = new linkList(); for (int i = 0; i < 10; i++) {// for (int i = 10; i > 0; i--) { myList.insert(i); } myList.printList(); }}