为何代码持续抛出java.lang.StringIndexOutOfBoundsException异常？

我写了一个方法，本意是把字符串数组playlist1d按每个|分割后存入二维数组playlist2d，但一直抛出异常。异常出现在第一个if语句下的temp = playlist1d[counter].charAt(characterCount);行。我尝试在while循环里加col<=5的条件，想让col超过5就停止循环，但它还是会跑到6触发错误。改成col<5能正常运行，但col<6或col<=5都没用。

原数组代码 #

private static String[] playlist1d = new String[] {
            "List | Title | Artist | Album | Genre | Rating | ",
            "1 | qwer | asd | zxcv | asdf | 2 | ",
            "2 | wert | sdfg | xcvb | sfdg | 3 | ",
            "3 | erty | dfgh | cvbn | dfgh | 1 | ",
            "4 | qwer | asdf | zxcv | sedfg | 5 | ",
            "5 | wert | sdf | asdf | qwer | 4 | ",
            "6 | poij | wert | asdf | bsfs | 4 | ",
            "7 | test | fdsf | gfddg | oij | 4 | ",
            "8 | tret | gfgd | sdfd | we | 1 | ",
            "9 | t | s | d | f | 4 | ",
            "10 | poij | wert | sdfgshdg | a | 2 | ",
            "11 | qer | asdaf | tsth | sf | ",
            "12 | qwer | asdf | zxcv | asfd | 2 |"
    };

注：lineCount和songCount均为数组行数13，目标二维数组playlist2d为[13][6]结构。

出现异常的方法代码 #

public String[][] charCounterRow(int songCount, String[] playlist1d)throws IOException{
        Character temp;
        int characterCount=0, col = 0, rowLength, nullCount=0;
        String playlist2d[][] = new String[lineCount][6];
        String tempLine = "|", tempString;
        for(int counter = 0; counter < lineCount; counter++){
            temp = playlist1d[counter].charAt(characterCount);
            tempString = String.valueOf(temp);
            rowLength = playlist1d[counter].length();
            while(characterCount < rowLength && col <= 5){
                if(tempString.equals(tempLine)){
                    characterCount++;
                    col++;
                    nullCount = 0;
                    temp = playlist1d[counter].charAt(characterCount);
                    tempString = String.valueOf(temp);
                }
                else if(!tempString.equals(tempLine)){
                    if(nullCount == 0){
                        playlist2d[counter][col] = String.valueOf(temp);
                    }
                    else{
                        playlist2d[counter][col] += temp;
                    }
                    characterCount++;
                    temp = playlist1d[counter].charAt(characterCount);
                    tempString = String.valueOf(temp);
                    nullCount++;
                }
            }
            characterCount = 0;
            col=0;
        }
        return playlist2d;
    }

问题根源 #

1. 循环条件判断滞后：while循环的条件判断是在每次循环开始时，但当处理到第6个|时，col会先被递增到6，之后才会触发下一次循环的条件检查。而在col变为6之后，代码仍会执行charAt(characterCount)，如果此时characterCount已经到达字符串末尾，就会抛出索引越界异常。
2. 数据不兼容：数组第11行"11 | qer | asdaf | tsth | sf | "只有5个有效字段，缺少Rating列数据，但原逻辑仍按6列处理，导致读取到字符串末尾时触发越界。
3. 手动解析易出错：逐字符解析的方式对索引控制要求极高，稍有不慎就会出现逻辑漏洞，不如Java内置的字符串分割方法可靠。

解决方案 #

方案1：使用内置split方法（推荐） #

直接用String.split()分割每行字符串，代码简洁且不易出错：

public String[][] splitPlaylist(int songCount, String[] playlist1d) throws IOException {
    String[][] playlist2d = new String[lineCount][6];
    for (int counter = 0; counter < lineCount; counter++) {
        // 按" | "分割，处理分隔符前后的空格
        String[] parts = playlist1d[counter].split(" \\| ");
        for (int col = 0; col < 6; col++) {
            // 字段不足时填充空字符串，避免null
            playlist2d[counter][col] = col < parts.length ? parts[col].trim() : "";
        }
    }
    return playlist2d;
}

方案2：修复原手动解析逻辑 #

如果坚持使用逐字符解析，需调整索引控制逻辑，避免col越界：

public String[][] charCounterRow(int songCount, String[] playlist1d)throws IOException{
    Character temp;
    int characterCount=0, col = 0, rowLength, nullCount=0;
    String playlist2d[][] = new String[lineCount][6];
    String tempLine = "|", tempString;
    for(int counter = 0; counter < lineCount; counter++){
        rowLength = playlist1d[counter].length();
        characterCount = 0;
        col = 0;
        nullCount = 0;
        while(characterCount < rowLength && col <= 5){
            // 先判断索引合法性，再读取字符
            if(characterCount >= rowLength) break;
            temp = playlist1d[counter].charAt(characterCount);
            tempString = String.valueOf(temp);
            
            if(tempString.equals(tempLine)){
                characterCount++;
                // 仅当col未到5时才递增，避免超过数组列数
                if(col < 5){
                    col++;
                    nullCount = 0;
                } else {
                    // 已填满6列，直接跳出循环
                    break;
                }
            } else {
                if(nullCount == 0){
                    playlist2d[counter][col] = String.valueOf(temp);
                } else {
                    playlist2d[counter][col] += temp;
                }
                characterCount++;
                nullCount++;
            }
        }
        // 填充缺失的列为空字符串
        for(; col < 6; col++){
            if(playlist2d[counter][col] == null){
                playlist2d[counter][col] = "";
            }
        }
    }
    return playlist2d;
}

内容的提问来源于stack exchange，提问作者Michael