java - 字符串替换方法不起作用

Question

public static String capitalise(String str)
{
     if (str != null || !"".equals(str))
     {
         char chr=str.charAt(0);
         String check= Character.toString(chr);
         String check1= check.toUpperCase();
         char chr1=check1.charAt(0);
         str.replace(chr, chr1);
         return str;            
    }
    else
    {
         System.out.println("Not a valid String");
    }

    return str;
}

Answer 1

您的问题是您没有从 str.replace 返回结果。字符串是不可变的

Answer 2

为什么你不简单地使用：

String str = "THIS IS my TEST strinG";
String my_string = str.substring(0,1).toUpperCase() + str.substring(1).toLowercase();

Answer 3

请确保您必须为 String 分配值

 str = str.replace(chr, chr1);

Answer 4

 str.replace(chr, chr1);

Returns a new string resulting from replacing all occurrences of oldChar in this string with newChar. replace
But you are not storing that value. So you can use following code

str = str.replace(chr, chr1);