Cannot reference a field before it is * defined" error

问题

public class Test1 {
 static{
    a=20;  
 //  System.out.println(a); //Line 4
    }
    static int a=getA();

private static int getA() {
    return 10;
}
public static void main(String[] args) {
    System.out.println(a);
}
}

Why it showing error ?but if remove the Line working fine ?

回答1:

It works if you declare a before the static initializer:

public class Test1 {
    static int a=getA();
    static{
        a=20;  
        System.out.println(a);
    }

    private static int getA() {
        return 10;
    }
    public static void main(String[] args) {
        System.out.println(a);
    }
}

Static initialization is done in the order it's written in the code. That means that in your code, you first set a to 20 and then initialize it to getA() - which is just as illegal as if you would have done it inside a function.

回答2:

Order matters.

static fields, block executes based on the order they placed in source code.

Move the declaration up . So that It can available to below blocks.

来源：https://stackoverflow.com/questions/22198527/cannot-reference-a-field-before-it-is-defined-error