So lösen Sie das Problem illegaler Vorwärtsreferenzen in Java

class BB
{
    static int a = 0 ;
    public BB()
    {
        a++ ;
        System.out.println("执行BB" + a) ;
    }
    public void printA()
    {
        System.out.println("a= " + a) ;
    }
}
public class CC
{
    static
    {
        a = new BB() ;
        a.printA() ;　　　　//报错说非法的前向引用
    }
    static BB a = new BB() ;
    public staic void main(String args[])
    {
        CC c = new CC() ;
    }
}

class UseBeforeDeclaration
{
    static
    {
        x = 100;
        // ok - assignment , 赋值表达式的左值
        int y = x + 1;
        // error - read before declaration , 赋值表达式的右值
        int v = x = 3;
        // ok - x at left hand side of assignment , 左值
        int z = UseBeforeDeclaration.x * 2;
        // ok - not accessed via simple name , 是通过类.静态变量 的形式访问, 而非直接简单访问
        Object o = new Object()
        {
            void foo()
            {
                x++;
            }
            // ok - occurs in a different class , 不是CC的代码块或成员初始化中,而是在一个全新的内部类的函数中
            {
                x++;
            }
            // ok - occurs in a different class , 在一个内部类的代码块中, 和上一个类似
        };
    }
    {
        j = 200;
        // ok - assignment
        j = j + 1;
        // error - right hand side reads before declaration , 第二个右值
        int k = j = j + 1;
        // error - illegal forward reference to j , 第三个是右值
        int n = j = 300;
        // ok - j at left hand side of assignment , 左值
        int h = j++; 
        // error - read before declaration , 右值, 并参与了自增运算
        int l = this.j * 3;
        // ok - not accessed via simple name 通过this.j进行访问, 非直接简单访问
        Object o = new Object()
        {
            void foo()
            {
                j++;
            }
            // ok - occurs in a different class
            {
                j = j + 1;
            }
            // ok - occurs in a different class
        };
    }
    int w = x = 3;
    // ok - x at left hand side of assignment
    int p = x;
    // ok - instance initializers may access static fields
    static int u =
        (new Object()
    {
        int bar()
        {
            return x;
        }
    }).bar();
    // ok - occurs in a different class
    static int x;
    int m = j = 4;
    // ok - j at left hand side of assignment
    int o =
        (new Object()
    {
        int bar()
        {
            return j;
        }
    }).bar();
    // ok - occurs in a different class
    int j;
}

privateinti=j;
privateintj=i;