我要在循环里面把最后的逗号给去掉，但是要报错，谁帮我看看

public static void main(String[] args) {
int[] indexValue = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42};
int count = (int) (Math.random() * 42);
System.out.println("取出数字个数：" + count);
int[] resultIndex = new int[count];
for (int i = 0; i < count; i++) {
int index = (int) (Math.random() * 42);
if (!containValue(resultIndex, index)) {
resultIndex[i] = index;
} else {
i--;
}
}
for (int i = 0; i < resultIndex.length; i++) {
int i1 = indexValue[resultIndex[i]];
String strResult = String.valueOf(i1);
StringBuffer buffer = new StringBuffer(strResult);

            buffer.append(",");
            if (',' == buffer.charAt(buffer.length() - 1))
                buffer = buffer.deleteCharAt(buffer.length() - 1);
            buffer.delete(buffer.lastIndexOf(","),buffer.length());
            System.out.print(buffer);
        }
    }
private static boolean containValue(int[] resultIndex, int index){
    for (int j = 0; j < resultIndex.length; j++){
        if (index == resultIndex[j]){
            return true;
        }
    }
    return false;
}

 /* package whatever; // don't place package name! */

import java.util.*;
import java.lang.*;
import java.io.*;

/* Name of the class has to be "Main" only if the class is public. */
class Ideone
{
public static void main(String[] args) {
int[] indexValue = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42};
int count = (int) (Math.random() * 42);
System.out.println("取出数字个数：" + count);
int[] resultIndex = new int[count];
for (int i = 0; i < count; i++) {
int index = (int) (Math.random() * 42);
if (!containValue(resultIndex, index)) {
resultIndex[i] = index;
} else {
i--;
}
}
StringBuffer buffer = new StringBuffer("");
for (int i = 0; i < resultIndex.length; i++) {
int i1 = indexValue[resultIndex[i]];
String strResult = String.valueOf(i1);

buffer.append(strResult);
            buffer.append(",");

            //else
            //buffer.delete(buffer.lastIndexOf(","),buffer.length());

        }
                    if (',' == buffer.charAt(buffer.length() - 1))
                buffer = buffer.deleteCharAt(buffer.length() - 1);
                System.out.print(buffer);
    }
private static boolean containValue(int[] resultIndex, int index){
    for (int j = 0; j < resultIndex.length; j++){
        if (index == resultIndex[j]){
            return true;
        }
    }
    return false;
}
}

https://ideone.com/zxsIhD

取出数字个数：25
34,39,5,9,7,35,11,19,32,41,27,6,33,17,42,25,37,3,26,22,21,13,18,8,24

buffer.delete(buffer.lastIndexOf(","),buffer.length());
这里错了，下标为-1了。

解决办法

             if (',' == buffer.charAt(buffer.length() - 1))
                buffer = buffer.deleteCharAt(buffer.length() - 1);
            else //加上
            buffer.delete(buffer.lastIndexOf(","),buffer.length());

结果：
取出数字个数：38
395163126362812932423740204112914273518372224381917262341213013251534

在线编译运行测试的网址：https://ideone.com/iME2v0

将if(',' == buffer.charAt(buffer.length() - 1)))改为if(",".equals(buffer.charAt(buffer.length() - 1)))即可。

  public static void main(String[] args) {
        int[] indexValue = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42};
        int count = (int) (Math.random() * 42);
        System.out.println("取出数字个数：" + count);
        int[] resultIndex = new int[count];
        for (int i = 0; i < count; i++) {
            int index = (int) (Math.random() * 42);
            if (!containValue(resultIndex, index)) {
                resultIndex[i] = index;
            } else {
                i--;
            }
        }
        StringBuffer buffer = new StringBuffer();
        for (int i = 0; i < resultIndex.length; i++) {
            int i1 = indexValue[resultIndex[i]];
            String strResult = String.valueOf(i1);
            buffer.append(strResult);

            buffer.append(",");
            //if (','==buffer.charAt(buffer.length() - 1))
                //buffer = buffer.deleteCharAt(buffer.length() - 1);
            //System.out.print(buffer);
        }
        buffer.delete(buffer.lastIndexOf(","),buffer.length());
        System.out.print(buffer);
    }
    private static boolean containValue(int[] resultIndex, int index){
        for (int j = 0; j < resultIndex.length; j++){
            if (index == resultIndex[j]){
                return true;
            }
        }
        return false;
    }