Labeled loop in Java

Question

I having been staring at my screen for a while and I do really need an explanation for labeled loop in this scenario:

package com.misterkourouma.oca8.starter.test; public class LabeledLoop{ public static void main(String[] args) { int x = 5, j = 0; OUTER: for (int i = 0; i < 3;) // -> This line has no curly braces but still compiles INNER: do { i++; x++; if (x > 10) break INNER; x += 4; j++; } while (j <= 2); System.out.println(x); } }

But this one does not compile :

package com.misterkourouma.oca8.starter.test; public class LabeledLoop2{ public static void main(String[] args) { int x = 5, j = 0; OUTER: for (int i = 0; i < 3;) System.out.println("Labeled Loop"); INNER: do { i++; x++; if (x > 10) break INNER; x += 4; j++; } while (j <= 2); System.out.println(x); } }

All the INNER: block are considered (I guess) as a single statement but It does not end with semicolon I wonder Why?

I am preparing for OCA 8 that's one of the reason I need to understand these weirds stuffs.

EDIT:
My question is on LabeledLoop example why does it compiles
Thanks in advance for your help.

codeLover · Accepted Answer · 2018-08-08 05:33:12Z

As per my understanding you would be getting the compilation error at the below statement:

 i++;

It is because of the fact that you are not creating any block at OUTER: for (int i = 0; i < 3;) statement(by using curly braces{}), thus, by default scope of the OUTER loop remains till the very next statement(in your case at System.out.println("Labeled Loop");). When you increment the variable i after three statements , it would be giving you compilation error, stating i is undeclared.

kourouma_coder · Accepted Answer · 2018-08-08 05:58:38Z

You have missed the {} braces around the for loop. That is the reason, the code is not compiling. It is not recognising the variable i. As i scope is

OUTER: for (int i = 0; i < 3;) { System.out.println("Labeled Loop") only public static void main(String[] args) { int x = 5, j = 0; OUTER: for (int i = 0; i < 3;) { System.out.println("Labeled Loop"); INNER: do { i++; x++; if (x > 10) break INNER; x += 4; j++; } while (j <= 2); System.out.println(x); } }

Nin · Accepted Answer · 2018-08-08 05:29:46Z

Curly Brackets are important in Java, while indents are not.

This code:

public static void main(String[] args) { int x = 5, j = 0; OUTER: for (int i = 0; i < 3;) System.out.println("Labeled Loop"); INNER: do { i++; x++; if (x > 10) break INNER; x += 4; j++; } while (j <= 2); System.out.println(x); }

means:

public static void main(String[] args) { int x = 5, j = 0; OUTER: for (int i = 0; i < 3;) System.out.println("Labeled Loop"); INNER: do { i++; x++; if (x > 10) break INNER; x += 4; j++; } while (j <= 2); System.out.println(x); }

which, of course does not compile.

GiorgosDev · Accepted Answer · 2018-08-08 05:33:22Z

If there are no braces after for loop - it is considered that only the first expression is inside the loop. so the first example is equivalent to

 OUTER: for (int i = 0; i < 3;){ INNER: do { i++; x++; if (x > 10) break INNER; x += 4; j++; } while (j <= 2); } System.out.println(x);

The variable i is declared in the for loop. In the first example do-while is inside of for loop so everything is ok. The second example is equivalent to

 OUTER: for (int i = 0; i < 3;){ System.out.println(x); } INNER: do { i++; x++; if (x > 10) break INNER; x += 4; j++; } while (j <= 2);

So variable i occurs out of scope and not declared in the while loop

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