今天又碰到一个新BUG,记下来。
一直报空指针异常,我就很奇怪了,怎么就空指针了呢,我输出时,也能输出东西呀。
原来Arrays.sort() 和 Collections.sort() 都是对整个数组或者链表进行排序的,也就是整个数组或者链表有多长就会进行多长的排序。
而我new的数组时30,而真正new的对象只有20个,故后10个对象没有实例化,而排序比较时有用到,故会报空指针异常。
import java.util.ArrayList; import java.util.Arrays; import java.util.Collections; import java.util.Comparator; import java.util.List; import java.util.Scanner; public class Main { public static <T> void main(String[] args) { Scanner cin = new Scanner(System.in); // 对象链表排序 List<People> list = new ArrayList<People>(); for(int i = 0; i < 20; i++) { list.add(new People(20 - i, "ys" + i)); } Collections.sort(list, new Comparator<People>() { @Override public int compare(People arg0, People arg1) { // TODO Auto-generated method stub return arg0.age - arg1.age; } }); for(int i = 0; i < 20; i++) { System.out.println(list.get(i).age + list.get(i).name); } // 对象数组排序 People[] peos = new People[20]; for(int i = 0; i < 20; i++) { peos[i] = new People(20 - i, "; song-" + i); } Arrays.sort(peos, new Comparator<People>() { @Override public int compare(People o1, People o2) { // TODO Auto-generated method stub System.out.println(o1.name); return o1.age - o2.age; } }); System.out.println("==================="); for(int i = 0; i < 20; i++) { System.out.println(peos[i].age + peos[i].name); } } } class People{ int age; String name; People(int age, String name){ this.age = age; this.name = name; } }