java - Is it necessary to make immutable class as final

Question

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why to declare immutable class as final in java

Why declare an immutable class as final in Java ? Please explain with some example if it is really necessary to declare it as final (consider all fields to be private and that the class has no setter methods).

Answer 1

首先这是什么是不可变的

Immutable means that once an object of that Class has been created
it can't be altered.
Ex: String class

第二件事如何使类不可变。

1. 使课程最终
2. 使所有成员成为最终成员，在静态块中或在构造函数中显式设置它们
3. 将所有成员设为私有
4. 没有修改状态的方法