Java String.concat() 不进行连接
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String.concat() doesn't do concatenation
提问by
I am trying to concatenate a String with an int and char including spaces, but not getting any concatenation. What is the reason?
我试图将一个字符串与一个包含空格的 int 和 char 连接起来，但没有得到任何连接。是什么原因？
private String messages;
Random r = new Random();
int random = r.nextInt(1000);
char ch='s';
messages.concat(String.valueOf(random));
messages.concat(" ");
messages.concat(String.valueOf(ch));
messages.concat(" ");
采纳答案by ssantos
concatdoes not alter the invoking strings, but returns a new one.
concat不会改变调用字符串，而是返回一个新字符串。
You may assign each resulting Stringto your result like this.-
您可以String像这样将每个结果分配给您的结果。-
messages = messages.concat(String.valueOf(random));
messages = messages.concat(" ");
messages = messages.concat(String.valueOf(ch));
messages = messages.concat(" ");
Or just use the overloaded operator +
或者只使用重载运算符 +
messages = String.valueOf(random) + " " + String.valueOf(ch) + " ";
回答by Cruncher
messages += String.valueOf(random) + " " + String.valueOf(ch) + " ";
回答by Reimeus
Stringsare immutable. You can either append the result using Stringconcatenation as shown in other answers or you can use StringBuilder
Strings是不可变的。您可以使用String连接附加结果，如其他答案所示，或者您可以使用StringBuilder
StringBuilder messages = new StringBuilder();
messages.append(String.valueOf(random));
messages.append(" ");
messages.append(String.valueOf(ch));
messages.append(" ");
Have a look at How do I concatenate two strings in Java?
Edit:(to insert at beginning of String)
编辑：（在开头插入String）
messages.insert(0, "newstring");
回答by Ahmed Adel Ismail
char ch='s';
messages = messages.concat(String.valueOf(random));
messages = messages.concat(" ");
messages = messages.concat(String.valueOf(ch));
messages = messages.concat(" ");
String should be RE-Assigned, when you edit a String object, you create a new String Object in the String constant pool, but you didnt assign this new String value to any reference variable, so you will need to re-assign your modifications to the SAME REFERENCE VARIABLE that created them
String 应该是 RE-Assigned，当你编辑一个 String 对象时，你在 String 常量池中创建了一个新的 String 对象，但是你没有将这个新的 String 值分配给任何引用变量，所以你需要将你的修改重新分配给创建它们的相同引用变量
回答by Stathis Andronikos
A better way is :
更好的方法是：
Random r = new Random();
int random = r.nextInt(1000);
StringBuilder str = new StringBuilder(String.valueOf(random));
str.append("s")
str.append(String.valueOf(random))
str.append(" ");
str.append(String.valueOf(ch));
