Java字符串是不可变的吗? [英] Is Java String immutable?

问题描述

我不理解此代码，为什么我的字符串c不能在main方法中更改而在changeString中更改.你能解释一下吗?

I don't understand this code, why my string c don't changing in main method but changing in changeString. Can you explain me?

class MainClass {
    public static void main(String[] args) {
        String c = "lalala";
        changeString(c);
        System.out.println("str in main = "+c);
    }

    public static void changeString(String str) {
        str = str + "CHANGE!!!";
        System.out.println("str in changeString = "+str);
    }

}

结果:

str in changeString = lalalaCHANGE!!!
str in main = lalala

推荐答案

是的，java字符串是不可变的.

Yes, the java string is immutable.

在changeString中，您传递了对字符串lalala的引用，然后将 reference 更改为指向lalalaCHANGE!!!的引用.原始字符串对象未更改，main中的引用仍引用该原始对象.

In changeString, you are passing in a reference to the string lalala and then you are changing the reference to one that points to lalalaCHANGE!!!. The original string object is not changed, and the reference in main still refers to that original object.

如果要使用StringBuilder而不是字符串，并将CHANGE!!!附加到该StringBuilder，那么您将在main上查看它时看到更改:

If you were to use a StringBuilder instead of a string, and append CHANGE!!! to that StringBuilder, then you would see the change reflected in viewing it at main:

class MainClass {
    public static void main(String[] args) {
        StringBuilder c = new StringBuilder("lalala");
        changeString(c);
        System.out.println("str in main = "+c.toString());
    }

    public static void changeString(StringBuilder str) {
        str.append("CHANGE!!!");
        System.out.println("str in changeString = "+str.toString);
    }

}

在此更改的版本中，您将获得:

In this changed version you would get:

str in changeString = lalalaCHANGE!!!
str in main = lalalaCHANGE!!!

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