Apex Loops
Loops are used to repeat a block of code multiple times. Instead of writing the same lines again and again, loops allow you to automate repetition based on a condition.
In Apex, the most commonly used loops are:
• for loop
• while loop
• do-while loop
1. for Loop
The for loop is used when you know how many times you want to run the code.
Syntex:
for (initialization; condition; update) {
// Code to repeat
}
| Part | Description |
|---|---|
| Initialization | Starting point (e.g., int i = 0) |
| Condition | Checked before each loop |
| Update | Changes the loop variable (i++) |
Example:
for (Integer i = 1; i <= 5; i++) {
System.debug(‘Number: ‘ + i);
}
Code Explanation:
• Integer i = 1: Initializes a counter variable i with value 1.
• i <= 5: Loop runs as long as i is less than or equal to 5.
• i++: Increments i by 1 after each loop iteration.
• System.debug(‘Number: ‘ + i);: Prints the current value of i with the prefix ‘Number: ‘.
Output:
Number: 1
Number: 2
Number: 3
Number: 4
Number: 5
2. while Loop
The while loop is used when you don’t know the exact number of repetitions, but want to loop as long as a condition is true.
Syntex:
while (condition) {
// Code to repeat
}
Example:
Integer i = 1;
while (i <= 3) {
System.debug(‘Count: ‘ + i);
i++;
}
Code Explanation:
• hile (i <= 3): The loop continues to run as long as i is less than or equal to 3.
• System.debug(‘Count: ‘ + i);: Prints the current value of i with the prefix ‘Count: ‘.
• i++;: Increments i by 1 after each iteration to move toward the loop’s exit condition.
Output:
Count: 1
Count: 2
Count: 3
3. do-while Loop
This is like the while loop, but it always executes at least once, even if the condition is false.
Syntex:
do {
// Code to repeat
} while (condition);
Example:
Integer i = 5;
do {
System.debug(‘Hello: ‘ + i);
i–;
} while (i > 3);
Code Explanation:
• Integer i = 5;: Initializes a counter variable i with value 5.
• do { … } while (i > 3);:
• The do block runs at least once, even if the condition is false
• After executing the block, the condition i > 3 is checked.
• If true, the loop repeats.
• System.debug(‘Hello: ‘ + i);: Prints the current value of i with the prefix ‘Hello: ‘.
• i–;: Decrements i by 1 after each iteration.
Output:
Hello: 5
Hello: 4
Key Difference: while checks before running; do-while checks after running once
Code Example
1. for loop for Sum
Integer sum = 0;
for (Integer i = 1; i <= 5; i++) {
sum += i;
}
System.debug(‘Sum = ‘ + sum);
Code Explanation:
• Integer sum = 0;: Initializes a variable sum to store the total, starting at 0.
• for (Integer i = 1; i <= 5; i++): • Loop starts with i = 1 and continues while i <= 5, incrementing i by 1 each time.
• sum += i;: Adds the current value of i to sum during each loop iteration.
• System.debug(‘Sum = ‘ + sum);: Prints the final value of sum after the loop ends.
Output:
Sum=15
2. while loop for Countdown
Integer count = 3;
while (count > 0) {
System.debug(‘Countdown: ‘ + count);
count–;
}
Code Explanation:
• Integer count = 3;: Initializes a counter variable count with value 3.
• while (count > 0): The loop runs as long as count is greater than 0.
• System.debug(‘Countdown: ‘ + count);: Prints the current value of count with the prefix ‘Countdown: ‘.
• count–;: Decreases count by 1 after each iteration to move toward ending the loop.
Output:
Countdown: 3
Countdown: 2
Countdown: 1
.3. do-while loop with Condition False
Integer num = 0;
do {
System.debug(‘This runs at least once.’);
} while (num > 0);
Code Explanation:
• Integer num = 0;: Initializes the variable num with value 0.
• do { … } while (num > 0);:
• The code inside the do block runs once before the condition is checked.
• After the first execution, the condition num > 0 is false, so the loop stops.
• System.debug(‘This runs at least once.’);: Prints a message showing that the block executes at least once, regardless of the condition.
Output:
This runs at least once.
