Keyword

static, final, volatile

static vs. final

• The static member can be accessed before the class object is created.

• `static` is used to define the class member that can be used independently of any object of that class

• Final keyword is used to declare, a constant variable, a method which can not be overridden and a class that can not be inherited.

import java.util.ArrayList;
import java.util.List;

class Test {
    private final List foo;

    public Test() {
        foo = new ArrayList();
        foo.add("foo"); // Modification-1
    }

    public void setFoo(List foo) {
       //this.foo = foo; Results in compile time error.
    }
}

volatile

1. 在写入 volatile 变量时，之前写的（在缓存里的）变量都会被强制写入内存中

2. 在读取 volatile 变量时，之前读的（在缓存里的）变量都会重新从内在中读取