EMZETT.Loops
In short: Java provides three loop types for executing code repeatedly: for, while, and do...while — depending on whether the number of iterations is known in advance or depends on a condition at runtime.
In more detail: The choice of loop type depends on when the exit condition is checked: pre-test loops (for, while) check before every iteration, the post-test do...while loop always executes the body at least once. break and continue additionally control the flow within a loop.
In Depth
| Loop | Control | Check timing | Typical use |
|---|---|---|---|
for | pre-test | before every iteration | fixed/known number of iterations |
for-each | pre-test | per element | iterate over an array/collection |
while | pre-test | before every iteration | unknown number, condition-dependent |
do-while | post-test | after every iteration | at least 1 iteration guaranteed |
// Classic for loop - when the number of iterations is known in advance
for (int i = 0; i < 5; i++) { System.out.println(i); }
// while - when it's unclear how often the loop will run
int n = 100;
while (n > 1) { n = (n % 2 == 0) ? n / 2 : n * 3 + 1; } // Collatz sequence
// for-each - iterate over elements instead of indices
for (String name : List.of("Anna", "Ben")) { System.out.println(name); }Choosing the right loop type is more than pure taste: a for loop immediately signals to the reader “a known, fixed number of iterations runs here” (e.g. exactly 5 times), a while loop signals “the number here depends on a runtime condition” (the Collatz example above can theoretically run for an arbitrarily long time). A for-each should always be chosen when you just want to iterate over ALL elements of a collection, with no need for the index itself — it’s less error-prone (no off-by-one risk) than an index-based for loop.
See also: For Loop, While Loop, do-while Loop, Break/Continue