While loops

Intermediate Java

Jim White

Java Developer

How while loop works

First check condition
- If true, we run the code provided
- If not, the loop ends
Repeat: check condition and then decide

Schema for while loop

while loop syntax

while (condition) {

  // Run this code

}

Syntax similar to if statement
Unlike if statement, can run multiple times

while loop example

// Prints numbers smaller than 5
int counter = 1;

while (counter < 5){
  System.out.println(counter);
  counter = counter + 1;
}

Infinite while loop

Forgot to update variable

int counter = 1;

while (counter < 5){
  System.out.println(counter);
  counter = counter + 0;
}

➡ Causes program to hang

Condition is always true

int counter = 1;

while (counter < 5){
  System.out.println(counter);
  counter = counter - 1;
}

Updating operators

int counter = 0;

// Same as counter = counter + 3
counter += 3;

Similar to -=, *=, /=, ...

Break

We can use break to exit while loop early, but not best coding practice

int counter = 0;
while (counter < 5){
    System.out.println("Counter: " + counter);
    if (counter == 3) {
        break; // Exit the loop when counter is 3
    }
    counter+=2;
}

Counter: 1
Counter: 3

Recap

// while loop that prints even numbers smaller than 20
int counter = 2;

while (counter < 20){
  System.out.println(counter);
  counter *= 2;

  // Exit while loop if counter is odd
  if (counter % 2 == 1){ // counter % 2 is counter modulo 2
    System.out.println("Something went wrong, counter is odd.");
    break;
  }
}

Let's practice!

Intermediate Java