如何在Java中使用子字符串方法

Question

I have 3 strings:

String text1 = "abcdefgh";
String text2 = "abcdefghijklmn";
String text3 = "abcdefg";

and i want to do something like this:

text1.substring(int1, int2);
text2.substring(int1, int2);
text3.substring(int1, int2);

that would return abc(the first 3 characters) the problem is that the strings length is always changing, so i can't use text1.length no matter what.

Answer 1

If the length is changing, do a check first

if (textStr != null && textStr.length() >= 3) {
    newStr = textStr.substring(0, 3);
}

Answer 2

找到了答案：

.substring(0, 3)

Answer 3

Because the string length can vary (or perhaps even be null) you'd be better off writing something a little more general purpose. In your example your test strings are always longer than 3 characters, but is that always the case? You could also write this function to automatically pad the string to your desired length.

public static String variableLengthSubstring(String text, int length) {
    StringBuilder substring = new StringBuilder();
    if(text != null) {
        int i = 0;
        length = Math.min(length, text.length());
        while(substring.length() < length) {
            substring.append(text.charAt(i++));
        }
    }
    return substring.toString();
}