Do–while loop in Java - Step-by-Step Execution

Concept Flow - Do–while loop

Start

↓

Execute body

↓

Check condition

↓

Exit

The do-while loop runs the code inside the loop first, then checks the condition. If true, it repeats; if false, it stops.

Execution Sample

Java

int i = 1;
do {
  System.out.println(i);
  i++;
} while (i <= 3);

Prints numbers 1 to 3 by running the loop body first, then checking if i is less than or equal to 3.

Execution Table

Step	i value	Condition (i <= 3)	Action	Output
1	1	true	Print 1, increment i to 2	1
2	2	true	Print 2, increment i to 3	2
3	3	true	Print 3, increment i to 4	3
4	4	false	Exit loop

💡 i becomes 4, condition 4 <= 3 is false, loop stops

Variable Tracker

Variable	Start	After 1	After 2	After 3	Final
i	1	2	3	4	4

Key Moments - 3 Insights

Why does the loop body run even when the condition is false at the start?

Because the do-while loop runs the body first before checking the condition, as shown in step 1 of the execution_table.

When does the condition get checked in a do-while loop?

The condition is checked after the loop body runs, as seen between steps 1 and 2 in the execution_table.

What happens if the condition is false after the first iteration?

The loop stops immediately after the first iteration, as shown in step 4 where the condition is false and the loop exits.

Visual Quiz - 3 Questions

Look at the execution_table, what is the value of i at step 3?

A 4

B 2

C 3

D 1

💡 Hint

Check the 'i value' column at step 3 in the execution_table.

At which step does the condition become false and the loop stops?

A Step 4

B Step 2

C Step 3

D Step 1

💡 Hint

Look at the 'Condition' column in the execution_table to find when it is false.

If the initial value of i was 5, how many times would the loop body run?

A 0 times

B 1 time

C 5 times

D Infinite times

💡 Hint

Remember the do-while loop runs the body once before checking the condition.

Concept Snapshot

do-while loop syntax:
 do {
   // code
 } while (condition);

Runs loop body first, then checks condition.
Repeats if condition true, stops if false.
Always runs at least once.

Full Transcript

A do-while loop in Java runs the code inside the loop first, then checks the condition. If the condition is true, it repeats the loop. If false, it stops. This means the loop body always runs at least once, even if the condition is false at the start. For example, starting with i=1, the loop prints i and increments it until i is greater than 3. The execution table shows each step: printing the value, incrementing, checking the condition, and finally exiting when the condition fails. This helps beginners see how the loop runs and when it stops.