静态方法中变量的永久更改

Question

Let's say I have a public class with static methods, one of them for example:

 public static void test(boolean b){
   b = !b;
 }

Let's say this class name is Test. From another class, where I have a variable boolean a = false, I call

 Test.test(a);

How can I make it change a permanently, and not just change it in that static methods scope?

Answer 1

The only way to make the change permanent is to let the method have a return value and assign it to the variable :

public static boolean test(boolean b){
   return !b;
}

a = Test.test(a);

Answer 2

Use a static field:

public static boolean flag;

public static void test(boolean b){
    flag = !b;
}

Then:

boolean a = true;
Test.test(a);

System.out.println( Test.flag); // false

Answer 3

in your Test class you can define the boolean variable as static

public static boolean a;

and outside the class change or access it using Test.a=false; or a=Test.a

and if you need to use methods you can hide the static method with inheritance:

public class HideStatic {     
public static void main(String...args){  
    BaseA base = new ChildB();  
    base.someMethod();        
}  
}  

class BaseA {         
    public static void someMethod(){  
        System.out.println("Parent method");  
    }  
}  

class ChildB extends BaseA{  
    public void someMethod(){  
        System.out.println("Child method");  
    }  
}

Answer 4

You can pass an instance to method and use setters to change more variables at once.

public static void updateData(MyClass instance) {
    instance.setX(1);
    instance.setY(2);
}

Answer 5

I think you are asking for call by reference . You can get this in Java by using arrays:

public static void test(boolean[] b){
b[0] = !b[0];
}

boolean[] param = new boolean[] {a};
test(param);
a=param[0];
//a changed

This works, but it is ugly. If you need to return more than one value, have a look at the Pair or Tuple structures.

Answer 6

Sounds to me like you are looking for a Mutable Boolean , the simplest of which is an AtomicBoolean .

private void changeIt(AtomicBoolean b) {
    b.set(!b.get());
}

public void test() {
    AtomicBoolean b = new AtomicBoolean(false);
    changeIt(b);
    System.out.println(b);
}