java - 为什么下面的代码中出现错误 "Syntax error on token "println", = Expected"？

Question

在下面的代码中我添加了一些System.out.println语句，以便我每次都能看到变量值的变化。但我现在遇到错误“ token “println”上的语法错误，=预期”，尽管我检查了所有内容并且没有发现任何错误。在添加那些 System.out.println 语句之前，一切正常。

这是我的代码:

public class A{
  public static int temp = 4;
  //System.out.println("temp = "+temp);

  public int sum;
  System.out.println("sum = " + sum);
  public int y;
  System.out.println("y = " + y);
  public A(int x){
    y = temp - 2 +x;
    System.out.println("y = " + y);
    sum = temp + 3;
    System.out.println("sum = " + sum);
    temp-=2;
    //System.out.println("temp = "+temp);
  }
  public void methodB(int m, int n){
    int x = 0;
    y = y + m + (temp++);
    System.out.println("y = " + y);
    x = x + 2 +  n;
    System.out.println("x = " + x);
    sum = sum + x + y;
    System.out.println("sum = " + sum);
    System.out.println(x + " " + y+ " " + sum); 
  }


}


class B extends A {
  public int x;
  public int sum;
  System.out.println("sum = "+sum);
  public B(int p){
    super(p);
    y = temp + p ;
    System.out.println("y = "+y);
    sum = p+ temp + 1;
    System.out.println("sum = "+sum);
    temp-=1;
  }  
  public void methodB(int m, int n){    
    int  y =0;
    y = y + this.y; 
    System.out.println("y = " + y);
    x = this.y + 2 + temp;
    System.out.println("x = " + x);
    super.methodB(x, y);
    sum = x + y + super.sum;
    System.out.println("sum = " + sum);
    System.out.println(x + " " + y+ " " + sum);
  }


}

class Test
{
    public static void main(String [] args){
    A a1 = new A(2);
    B b1 = new B(3);
    a1.methodB(1, 1);
    b1.methodB(1, 2);
    a1.methodB(3, 2);
    b1.methodB(2, 2);

  }
}

Answer 1

不能在方法之外使用打印语句。在A类

System.out.println("temp = " + temp);
System.out.println("sum = " + sum); 
System.out.println("y = " + y);

需要移动到方法中。 B类

System.out.println("sum = " + sum);

需要移动到方法中。

如果您想查看这些变量的默认值是什么，只需将这些打印语句首先放入构造函数中即可，如下所示

public A(int x){
    System.out.println("temp = " + temp);
    System.out.println("sum = " + sum); 
    System.out.println("y = " + y);

    y = temp - 2 + x;
    System.out.println("y = " + y);
    sum = temp + 3;
    System.out.println("sum = " + sum);
    temp -= 2;
    //System.out.println("temp = " + temp);
}