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help on this scope question

help on this scope question# Java - 爪哇娇娃

l*r2003-07-29 07:07

1 楼

I have two pieces of code
1) has compilation error:
class TestScope {
public void test() {
int x = 2;
if ( true ) {
int x = 1;
System.out.println( "In if: " + x );
}
System.out.println( "Out If: " + x );
}
}
2) compiled and output is: In if: 1 Out If: 2
class TestScope {
int x = 2;
public void test() {
if ( true ) {
int x = 1;
System.out.println( "In if: " + x );
}
System.out.println( "Out If: " + x );
}
}
Can you tell me why Java support this differently?
Thanks!

n*k2003-07-29 07:07

2 楼

~~~~~~~~~~~~
here is the compilation error
Because in the first example, there is no instance varible(or class variable)
nameed x exists other than the local varibale inside the method, so the scope
of the x is all over the method, and it can not be shadowed any other local
variable inside the method.
On the other hand, the second example has an instance variable x and also a
local block variable x, inside the if block, the local variable

【在 l***r 的大作中提到】

: I have two pieces of code
: 1) has compilation error:
: class TestScope {
: public void test() {
: int x = 2;
: if ( true ) {
: int x = 1;
: System.out.println( "In if: " + x );
: }
: System.out.println( "Out If: " + x );

h*b2003-07-29 07:07

3 楼

Nod, agree, very clear explanation!

variable)
scope

【在 n*****k 的大作中提到】

:
: ~~~~~~~~~~~~
: here is the compilation error
: Because in the first example, there is no instance varible(or class variable)
: nameed x exists other than the local varibale inside the method, so the scope
: of the x is all over the method, and it can not be shadowed any other local
: variable inside the method.
: On the other hand, the second example has an instance variable x and also a
: local block variable x, inside the if block, the local variable