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使用while循环、子字符串和indexOf的简单Java问题

indexof substring java

Ken Sinelli · 技术社区 · 4 年前

public static void main(String[] args) {
    
    String str = "We have a large inventory of things in our warehouse falling in "
            + "the category:apperal and the slightly "
            + "more in demand category:makeup along with the category:furniture and _.";
    
    printCategories(str);

}

public static void printCategories(String passedString) {
    
    int startOfSubstring = passedString.indexOf(":") + 1;
    int endOfSubstring = passedString.indexOf(" ", startOfSubstring);
    String categories = passedString.substring(startOfSubstring,endOfSubstring);
    
    while(startOfSubstring > 0) {
        System.out.println(categories);
        startOfSubstring = passedString.indexOf((":") + 1, passedString.indexOf(categories));
        System.out.println(startOfSubstring);
        System.out.println(categories);
    }

}

所以程序应该打印:

上诉
化妆
家具

一旦找不到“:”了,indexOf(startofstring的一部分)将返回-1,循环将终止。但是,在打印第一个类别之后,它会一直返回-1并在找到下一个类别之前终止。

        System.out.println(startOfSubstring);
        System.out.println(categories);

确认在打印第一个category之后返回-1,最后一行确认categories变量仍被定义为“apperal”。如果我把这句话注释掉:

startOfSubstring = passedString.indexOf((":") + 1, passedString.indexOf(categories));

它将startofstring返回为77。因此,这与该行有关,并试图更改indexOf方法中的搜索开始位置,这导致它过早地返回-1,但我无法理解为什么会发生这种情况。我花了几个小时想弄明白。。。

请帮忙:(

2 回复 | 直到 4 年前

Willis Blackburn 4 年前

该计划有几个问题:

passedString 对于 (":") + 1 哪根是弦 ":1" ,可能不是你想要的。
你应该评估一下 endOfSubstring 和 categories 在循环内。

public static void printCategories(String passedString) {
    
    int startOfSubstring = passedString.indexOf(":") + 1;
    
    while(startOfSubstring > 0) {
        int endOfSubstring = passedString.indexOf(" ", startOfSubstring);
        // If "category:whatever" can appear at the end of the string
        // without a space, adjust endOfSubstring here.
        String categories = passedString.substring(startOfSubstring, endOfSubstring);
        // Do something with categories here, maybe print it?
        // Find next ":" starting with end of category string.
        startOfSubstring = passedString.indexOf(":", endOfSubstring) + 1; 
    }

}

ControlAltDel 4 年前

while(startOfSubstring > 0) { // better if you do startOfSubstring != -1 IMO
    System.out.println(categories);
    // this should be startOfSubstring = passedString.indexOf(":", startOfSubstring +1);
    startOfSubstring = passedString.indexOf((":") + 1, passedString.indexOf(categories)); 
    System.out.println(startOfSubstring);
    System.out.println(categories);
}