Question

为什么提示java.lang.ArrayIndexOutOfBoundsException: -1 ???

用随机数产生彩票序列的小程序,为什么提示数组下标的问题呢???

import java.util.*;

public class LotteryDrawing {
public static void main(String[] args){
Scanner in = new Scanner(System.in);

System.out.print("要选几个数?");
int select_numbers = in.nextInt();

System.out.print("最大的数是多少?");
int all_numbers = in.nextInt();

int[] All_numbers = new int[all_numbers];
for(int i = 0; i < All_numbers.length; i++)
All_numbers[i] = i + 1;

int[] GuessResult = new int[select_numbers];
for(int j = 0; j < GuessResult.length; j++){
int r = (int)(Math.random() * all_numbers);

GuessResult[j] = All_numbers[r];

All_numbers[r] = All_numbers[all_numbers - 1];//此处报错

all_numbers--;
}
Arrays.sort(GuessResult);
System.out.println("我猜下面这几个能中~~~");
for(int r : GuessResult)
System.out.println(r);
}

}

Answer 1

for(int j = 0; j < GuessResult.length; j++){
int r = (int)(Math.random() * all_numbers);

GuessResult[j] = All_numbers[r];

All_numbers[r] = All_numbers[all_numbers - 1];//此处报错 当输入"最大的数"小于"要选的几个数"的时候，该for循环了GuessResult.length次，all_numbers-- 自减了GuessResult.length次，all_numbers-1，就会小于0了，All_numbers[all_numbers - 1]就会报ArrayIndexOutOfBoundsException啦

all_numbers--;
}

Answer 2

我猜 你选的数超过了最大数

追问

真没有……干嘛跟自己过不去啊…………