Does string really have to be immutable?

You may ask a person if the string is variable? Presumably they would all say the same. The string is immutable, because the string is final decorated, and it is the final modified char[] array at the bottom.

You can see the string source code:

public final class String    implements java.io.Serializable, Comparable<String>, CharSequence {    /** The value is used for character storage. */    private final char value[];

So the string is not to become, but we ignore the reflection, using reflection we can change the value of the string, say not much about how reflection is done:

public static void main(String[] args) throws Exception {        // 创建字符串"Hello World"， 并赋给引用s        String s = "Hello World";        //把这个s保存一份用于对比        String temp = s;        System.out.println("s和temp是否相等？ " + s.equals(temp));        System.out.println("s = " + s); // Hello World        // 获取String类中的value字段        Field valueFieldOfString = String.class.getDeclaredField("value");        // 改变value属性的访问权限        valueFieldOfString.setAccessible(true);        // 获取s对象上的value属性的值        char[] value = (char[]) valueFieldOfString.get(s);        // 改变value所引用的数组中的第5个字符        value[5] = '_';        System.out.println("s = " + s); // Hello_World        System.out.println("s和temp是否相等？ " + s.equals(temp));    }

We can see that we have used reflection to bypass the private permissions and modified the char[] array at the bottom of the string, and I want to read the little partner of this article. Do you know what to say when someone asks if the string is mutable?