Labeled break and continue in Java - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a labeled break in Java?

A labeled break allows you to exit a specific outer loop or block by using a label name before the break statement. It helps to break out of nested loops directly.

beginner

How does a labeled continue differ from a regular continue?

A labeled continue skips the current iteration of the specified outer loop, not just the innermost loop. It uses a label to identify which loop to continue.

intermediate

Example of labeled break usage:

outer: for (int i = 0; i < 3; i++) {
  for (int j = 0; j < 3; j++) {
    if (i == j) break outer;
  }
}

What happens when i equals j?

When i equals j, the labeled break 'break outer;' exits the outer loop completely, stopping all iterations of both loops.

beginner

Can you use labeled break or continue without nested loops?

Yes, but it is uncommon. Labeled break or continue is mainly useful for nested loops to control outer loops. Without nested loops, a label is unnecessary.

beginner

What is the syntax to define a label in Java?

A label is an identifier followed by a colon before a loop or block, for example:

labelName: for (int i = 0; i < 5; i++) { ... }

What does a labeled break do in nested loops?

A Restarts the entire program

B Exits the specified outer loop immediately

C Skips the current iteration of the innermost loop

D Does nothing special

A labeled break exits the loop identified by the label, which can be an outer loop in nested loops.

How do you write a label in Java?

A continue labelName;

B for (labelName) { ... }

C break labelName;

D labelName: for (...) { ... }

A label is an identifier followed by a colon placed before a loop or block.

What happens when you use labeled continue inside nested loops?

A Skips to the next iteration of the labeled outer loop

B Exits all loops immediately

C Skips the current iteration of the innermost loop only

D Causes a syntax error

Labeled continue skips the current iteration of the loop identified by the label.

Is it necessary to use labels with break or continue in single loops?

A Only for continue, not break

B Yes, always required

C No, labels are mainly for nested loops

D Only for break, not continue

Labels are useful mainly when you want to control outer loops in nested loops.

Which keyword is used to skip the current iteration of a loop?

A continue

B break

C exit

D skip

The continue keyword skips the current iteration and moves to the next iteration of the loop.

Explain how labeled break works in nested loops and give a simple example.

Think about how to stop multiple loops at once.

Describe the difference between labeled continue and regular continue in Java loops.

Focus on which loop is affected by the continue statement.

Practice

1. What does a labeled break statement do in Java nested loops?

easy

A. It skips the current iteration of the innermost loop.

B. It pauses the loop until a condition is met.

C. It restarts the innermost loop from the beginning.

D. It exits the loop identified by the label immediately.

Solution

1. Step 1: Understand labeled break usage

   A labeled break exits the loop that has the specified label, not just the innermost loop.

2. Step 2: Compare with normal break

   Normal break exits only the innermost loop, but labeled break can exit outer loops directly.

3. Final Answer:

   It exits the loop identified by the label immediately. -> Option D

4. Quick Check:

   Labeled break = exit labeled loop [OK]

Hint: Labeled break jumps out of the named loop instantly [OK]

Common Mistakes:

• Confusing labeled break with continue
• Thinking it only affects the innermost loop
• Assuming it pauses instead of exits

2. Which of the following is the correct syntax for a labeled continue statement in Java?

easy

A. continue: labelName;

B. continue labelName;

C. continue (labelName);

D. continue->labelName;

Solution

1. Step 1: Recall labeled continue syntax

   The correct syntax is the keyword continue followed by the label name and a semicolon.

2. Step 2: Eliminate incorrect forms

   Java does not use colons, parentheses, or arrows with continue statements.

3. Final Answer:

   continue labelName; -> Option B

4. Quick Check:

   Correct labeled continue syntax = continue labelName; [OK]

Hint: Use 'continue' followed by label and semicolon [OK]

Common Mistakes:

• Adding colon after continue
• Using parentheses around label
• Using arrow symbols instead of space

3. What is the output of the following Java code?

outer:
for (int i = 1; i <= 3; i++) {
    inner:
    for (int j = 1; j <= 3; j++) {
        if (j == 2) continue outer;
        System.out.print(i + "-" + j + " ");
    }
}

medium

A. 1-1 2-1 3-1 3-2

B. 1-1 1-2 1-3 2-1 2-2 2-3 3-1 3-2 3-3

C. 1-1 2-1 3-1

D. 1-1 2-1 2-2 3-1 3-2

Solution

1. Step 1: Analyze loops and continue

   When j == 2, the statement continue outer; skips the rest of the current outer loop iteration and moves to the next i.

2. Step 2: Trace output

   For i=1, j=1 prints "1-1 ". At j=2, continue outer skips to i=2. Similarly for i=2 and i=3, only j=1 prints.

3. Final Answer:

   1-1 2-1 3-1 -> Option C

4. Quick Check:

   Labeled continue skips to next outer loop iteration [OK]

Hint: Labeled continue skips to next iteration of labeled loop [OK]

Common Mistakes:

• Thinking continue skips only inner loop
• Expecting all inner loop values to print
• Ignoring label effect on continue

4. Identify the error in this Java code snippet using labeled break:

outer:
for (int i = 0; i < 3; i++) {
    for (int j = 0; j < 3; j++) {
        if (i == j) break;
    }
}

medium

A. The label 'outer' is not used with break or continue.

B. The break statement should be 'break outer;' to use the label.

C. Labels cannot be used with for loops.

D. The code will cause a syntax error due to missing semicolon.

Solution

1. Step 1: Check label usage

   The label 'outer' is declared but never referenced by break or continue statements.

2. Step 2: Understand label necessity

   Labels must be used with break or continue to have effect; otherwise, they are redundant but not syntax errors.

3. Final Answer:

   The label 'outer' is not used with break or continue. -> Option A

4. Quick Check:

   Unused label = no effect but no syntax error [OK]

Hint: Use label only if break or continue references it [OK]

Common Mistakes:

• Assuming unused label causes syntax error
• Thinking break without label breaks outer loop
• Confusing label usage rules

5. Given nested loops, how would you use labeled break and continue to print only pairs (i, j) where i < j, skipping all others efficiently? Choose the correct code snippet.

hard

A. outer:
for (int i = 1; i <= 3; i++) {
inner:
for (int j = 1; j <= 3; j++) {
if (i >= j) continue inner;
System.out.print("(" + i + "," + j + ") ");
}
}

B. outer:
for (int i = 1; i <= 3; i++) {
inner:
for (int j = 1; j <= 3; j++) {
if (i >= j) break outer;
System.out.print("(" + i + "," + j + ") ");
}
}

C. outer:
for (int i = 1; i <= 3; i++) {
inner:
for (int j = 1; j <= 3; j++) {
if (i >= j) continue outer;
System.out.print("(" + i + "," + j + ") ");
}
}

D. outer:
for (int i = 1; i <= 3; i++) {
inner:
for (int j = 1; j <= 3; j++) {
if (i >= j) break inner;
System.out.print("(" + i + "," + j + ") ");
}
}

Solution

1. Step 1: Understand the condition and loops

   We want to print pairs where i < j only. If i >= j, skip to next j (inner loop iteration).

2. Step 2: Analyze each option's control flow

   outer: for (int i = 1; i <= 3; i++) { inner: for (int j = 1; j <= 3; j++) { if (i >= j) continue inner; System.out.print("(" + i + "," + j + ") "); } } uses continue inner; to skip the current iteration and move to next j, efficiently skipping invalid pairs.

3. Final Answer:

   Uses continue inner; to skip when i >= j. -> Option A

4. Quick Check:

   Labeled continue to inner loop skips invalid pairs [OK]

Hint: Use 'continue inner;' to skip to next inner loop iteration [OK]

Common Mistakes:

• Using break outer which stops all loops
• Using continue outer which skips valid pairs as well
• Using break inner which stops inner loop prematurely