Java函数如何实现对字符串的截取

以下是一个Java函数，实现对字符串的截取1000字的功能：

public static String truncateString(String str) {
    if (str.length() <= 1000) {
        return str;
    }
    return str.substring(0, 1000);
}

该函数接收一个字符串参数str，如果str的长度小于或等于1000，则直接返回str原样；否则，使用substring()函数从str的第0个字符开始截取1000个字符，并返回截取后的字符串。

例如，对于输入字符串"This is a very long string that needs to be truncated to 1000 characters for example purposes."，该函数返回的字符串为"This is a very long string that needs to be truncated to 1000 characters for example purposes."（因为该字符串长度小于1000）；对于输入字符串"This is a very long string that needs to be truncated to 1000 characters for example purposes. This is more text that should be truncated."，该函数返回的字符串为"This is a very long string that needs to be truncated to 1000 characters for example purposes. This is more text that should be truncated."（因为该字符串长度大于1000，被截取前1000个字符）。