Can label be placed before switch?

[Gary Kevin]

K&B book:
"it's most common to use labels with loop statements like for or while,in conjunction with break and continue statements.A label statement must be placed just before the statement being labeled,and it consists of a valid identifier that ends with a colon( "

   
public class Demo{
public static void main(String[] args){
for(int i =0;i < 3;i++){
label1:
switch(i){
   case 0:System.out.println("34");
   case 1:System.out.println("23");break;
   case 2:System.out.println("12");
   case3:System.out.println("01");break label1;
   default:System.out.println("40");
}
}
}
}
 

This code compiles and runs well.Can label be placed before switch?

[Campbell Ritchie]

A label is not executable code, so you can put labels in all sorts of places.

Why you should want a label, now that's a different matter, unless it's "I just wanted to see what would happen," which is an adequate justification for anything, never mind how daft.

[Gary Kevin]

Originally posted by Campbell Ritchie:
A label is not executable code, so you can put labels in all sorts of places.

Why you should want a label, now that's a different matter, unless it's "I just wanted to see what would happen," which is an adequate justification for anything, never mind how daft.

I don't think so,label can't be put any sorts of places:

  
import java.util.*;
public class Demo{
public static void main(String[] args){

label1:
System.out.println("gdsfdf");

for(int i =0;i < 3;i++){
switch(i){
case 0:System.out.println("34");
case 1:System.out.println("23");break;
case 2:System.out.println("12");
case 3:System.out.println("01");break label1;
default:System.out.println("40");
}
}
 
}
}
 

it compiles error.label can only be put before for or while.
This is a SCJP question,so I'm confused about that.

[Ivan Ivanic]

you can put label before any statement or block of code.
but you cannot call break labelX if you are not in its scope.
you are trying to call break label1 in switch case 3 but it is out of scope.
look this code about scopes:

 label1:
System.out.println("in label1");//here scope of this label is
                                //this one statement so you can't
                                //break
 
label2:{  //here starts scope of label2
   System.out.println("label 2 started");
   break label2;  // here you can use break in scope of this label
   System.out.println("label 2 ended");  //but it wont compile because compiler
                                         //knows this statement is unreachable
}   //here ends scope of label2
 
break label2; // you cant do this here because you are out of scope
 
for(int i = 0; i < 5; i++){
   // bla bla bla
   break label2; // you cant do this here because you are out of scope

[Gary Kevin]

Originally posted by Ivan Ivanic:
you can put label before any statement or block of code.
but you cannot call break labelX if you are not in its scope.
you are trying to call break label1 in switch case 3 but it is out of scope.
look this code about scopes:

 label1:
System.out.println("in label1");//here scope of this label is
                                //this one statement so you can't
                                //break
 
label2:{  //here starts scope of label2
   System.out.println("label 2 started");
   break label2;  // here you can use break in scope of this label
   System.out.println("label 2 ended");  //but it wont compile because compiler
                                         //knows this statement is unreachable
}   //here ends scope of label2
 
break label2; // you cant do this here because you are out of scope
 
for(int i = 0; i < 5; i++){
   // bla bla bla
   break label2; // you cant do this here because you are out of scope

Ivan: is this means that if i put label just before for or while like

 
 label1:
  for(int i = 0; i < 5; i++){
      System.out.println("1");
      System.out.println("1");
      System.out.println("1");
      System.out.println("1");
  }
  
 

this label1 will implicitly add block?

 
 label1:{
  for(int i = 0; i < 5; i++){
      System.out.println("1");
      System.out.println("1");
      System.out.println("1");
      System.out.println("1");
  }
  }

[Ivan Ivanic]

well I guess you could say it like that. but that is the point.

[Gary Kevin]

Thinks all!