This lesson presents the final core computer capability: the ability to repeat something multiple times. By combining this with our ability to store and manipulate data and make decisions, we can truly solve any problem. So let’s get started!
Let’s meet our first loop.
It’s the simplest one in Java, and repeats a block of code
while a condition is
while loop declaration looks quite similar to the
if statements we’ve already seen.
First the keyword
while, followed by a conditional expression inclosed in parantheses, followed by a block.
However, unlike the
if statement which only executes once, the
while statement continues to execute the block as long as the condition evaluates to
This can cause problems!
while is the simplest loop, probably the most common loop you’ll encounter is called a
It’s more complicated than a
while loop, but designed to capture a common loop programming pattern.
We frequently want to use a loop to increment a variable starting at zero and ending when it reaches some value.
(We’ll see why tomorrow.)
This is so common that Java provides a second loop that captures this pattern. Let’s go through it together:
for loop syntax is quite flexible and can produce lots of different sequences of values in the index variable:
We can also omit one, two, or all three of the parts of a
for loop declaration:
However, by far the most common
for loop you’ll see is the start at 0, increment by 1, and end when the value is strictly less than some limit:
There is one important difference between this
Let’s try and figure out what it is!
Let's write a simple loop. Assuming an
int variable named
repeat has been declared and
initialized to a value larger than or equal to zero, write a loop that prints "Victory!"
repeat times on separate
lines. You may use any kind of loop you want! But do not modify the value of
Let’s explore the connection between the two types of loop using a diagram.
Let's write a simple loop.
int variable named
count has been declared and initialized to a value larger than zero, write a
loop that prints the numbers between 0 and
count - 1, inclusive, one number each line.
4, you should print:
0 1 2 3
You can use any kind of loop you want!
But do not modify
Need more practice? Head over to the practice page.