# Looping/Iterating

* [Looping/Iterating](/workspace/languages/java/beginner/looping.md#loopingiterating)
  * [What](/workspace/languages/java/beginner/looping.md#what)
  * [While](/workspace/languages/java/beginner/looping.md#while)
  * [Do While](/workspace/languages/java/beginner/looping.md#do-while)
  * [For](/workspace/languages/java/beginner/looping.md#for)
    * [Old/basic](/workspace/languages/java/beginner/looping.md#oldbasic)
    * [New/enhanced](/workspace/languages/java/beginner/looping.md#newenhanced)
  * [break statement](/workspace/languages/java/beginner/looping.md#break-statement)
  * [continue statement](/workspace/languages/java/beginner/looping.md#continue-statement)
  * [Recursion](/workspace/languages/java/beginner/looping.md#recursion)
  * [Nested loops](/workspace/languages/java/beginner/looping.md#nested-loops)
    * [Links](/workspace/languages/java/beginner/looping.md#links)
  * [for](/workspace/languages/java/beginner/looping.md#for)
  * [while](/workspace/languages/java/beginner/looping.md#while)
  * [do while](/workspace/languages/java/beginner/looping.md#do-while)
  * [break, continue](/workspace/languages/java/beginner/looping.md#break-continue)
  * [Nested loops](/workspace/languages/java/beginner/looping.md#nested-loops)
  * [other](/workspace/languages/java/beginner/looping.md#other)

## What

* Repeating the same task
* Doing the same thing across a data structure
* `for`/`while`/`do while` (imperative)

## While

* Format

```java
while(booleanExpression) {
  //body
}
```

* need to ensure that loop is terminated
  * what the booleanExpression is for
  * Can make booleanExpression = true, and loop will be infinite
    * but have a `break` in the body to exit the loop

## Do While

* Format -

  ```java
  do {
  //body
  } while(booleanExpression)
  ```
* similar to while loop, but always does one execution of the body first.

## For

### Old/basic

* Format -

  ```java
  for(initialization; booleanExpression; updateStatement) {
  //body
  }
  ```
* Not good for functional style as initialization has mutated variable.
* initialization can declared in the loop, and has scope just for the for loop.
  * Can declared outside of loop, initialized in loop and thus have scope inside nad outside of loop
  * If declared and init outside of loop, but reinit inside for loop, error will occur
* Inifinite loop `for(;;) { // body }`
* All components in for loop are optional
* Can have multiple initialization statements, booleanExpressions and updateStatements
  * Must have same data type in initialization

### New/enhanced

* aka for-each loop

  -format

```java
for (datatype instance : collection) {
  //body...
}
```

* `collection` must implement Iterable interface

  \-

## break statement

* using a label (which is optional)

```java
aLabel: while (x > 5) {
  // some logic
  while (x.isEven) {
    // some logic
    break aLabel;
  }
}
```

* This will break out of the top level loop instead of inner loop where the break is set.
  * used in while/do while/switch/ for

## continue statement

* finishes the flow of the current loop.
* Uses the same syntaz as that of break when using optional lables
* used in while/do while/for

## Recursion

* stackoverflow exception

## Nested loops

#### Links

## for

* <https://docs.oracle.com/javase/tutorial/java/nutsandbolts/for.html>
* <https://www.javatpoint.com/java-for-loop>
* <https://www.tutorialspoint.com/java/java_for_loop.htm>

## while

* <https://www.javatpoint.com/java-while-loop>
* <https://docs.oracle.com/javase/tutorial/java/nutsandbolts/while.html>
* <https://www.tutorialspoint.com/java/java_while_loop.htm>

## do while

* <https://www.javatpoint.com/java-do-while-loop>
* <https://www.tutorialspoint.com/java/java_do_while_loop.htm>

## break, continue

* <https://www.javatpoint.com/java-break>
* <https://www.javatpoint.com/java-continue>

## Nested loops

* <https://www.programiz.com/java-programming/nested-loop>

## other

* <https://stackoverflow.com/questions/8880870/java-for-vs-whiletrue>

  \-


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