abstract class abc{
int num;
int num1;
String name;

abc(){
}

abc(int n1,int n2,String name1){
num=n1;
num1=n2;
name=name1;
}

int sj(){
return num*num1;
}

abstract void sj2();
}

class a extends abc{
static int sum=0;

a(int n1,int n2,String name1){
super(n1,n2,name1);
}

void sj2(){
sum= num+num1;
}

public static void main(String []w)
{
a t=new a(2,9,"li");
System.out.println(t.sj());
System.out.println(sum);
// System.out.println(t.sj2());
}
}

打印SUM总是0，不知道为什么。

你的sj()的方法里面是

return num*num1;

它只是返回num*num1的值,并没有改变它们的值啊

恩,就是就是

function
void sj2(){
sum= num+num1;
}

没有被执行，静态变量当然值不会变化了；

debug:

abstract class abc{
int num;
int num1;
String name;

abc(){
}

abc(int n1,int n2,String name1){
num=n1;
num1=n2;
name=name1;
}

int sj(){
return num*num1;
}

abstract void sj2();
}

class a extends abc{
static int sum=0;

a(int n1,int n2,String name1){
super(n1,n2,name1);
}

void sj2(){
sum= num+num1;
}

public static void main(String []w)
{
a t=new a(2,9,"li");
System.out.println(t.sj());
System.out.println(a.sum);
t.sj2();
System.out.println(a.sum);

}
}