当我使用 a=x, b=y 时，结果是 15。但是当我使用 x=a,y=b 时，结果是 0。你能解释一下为什么吗？
public class Test {
int a , b;
Test(int x, int y) {
a=x;
b=y;
}
int sr() {
return a*b;
}
public static void main (String args[]){
Test t=new Test(5,3);
System.out.println(t.sr());
}
}
a=x;
b=y;
will set the instance attributes a & b values with the passed values x and y. so when you create an instance using :
Test t=new Test(5,3);
a and b will be have values 5 & 3 respectively. Hence calling method t.sr will return
a*b = 5*3 = 15;
On the other hand if u use:
x = a;
y = b;
local variables x and y will be set to with the default values of a and b i.e. 0. Also a and b will hold defualt values as 0 as no other value is set. So when u do
Test t=new Test(5,3);
as a & b have values 0 so calling method t.sr will return
a*b = 0*0 = 0;
int 字段的默认值为 0。因此，如果您不为它们分配值，则它们为 0。请参阅：http ://www.javapractices.com/topic/TopicAction.do?Id=14
In the constructor you are passing the value of x and y and storing it in a and b respectivey. Now when you call method a and b has got values so it returns the value of a*b.
Also a and b are class variables so it has got default values i.e a=0,b=0;
Now in the second case x=a,y=b. you are storing the values of a and b respectivey in x and y.As you are not storing the any values in a and b and again you are calling sr method so it only returns value of a and b i.e 0*0 so you get 0 as output
when you use x= a, y=b
you are not assigning values to a and b which was used in sr().
Since there are instance variable they will be assigned default value 0 and hence result is 0
when you use x=a, y=b x and y are local variables. They are discard as soon as that block(constructor) get executed. But a, b are instance variables. They exist until you have the instance from the class. Default value for int instances is 0; since you are not changing those values you always get 0
In the scope of the constructor, x and y are local variables.
If you do:
x = a;
y = b;
The member variables a and b are never initialized in your constructor. So doing a a * b will yield 0 as the default values for a and b is 0.
And really, it makes no sense to do x = a and y = b.