For Each

Java 5.0 added the enhanced for loop to make it easier to step through a collection, such as an array.

for (declaration : expression)
  statement;

The enhanced for loop is sometimes called the for each loop.

The for each loop iterates through each item in the collection, but does not use a control variable to do so. The example below shows a standard for loop, and then a for each loop that does the same task.

int[] odds = {1, 3, 5, 7};

for (int i=0; i < odds.length; i++){
  int num = odds[i];
  System.out.println(num);
}

for (int num : odds){
  System.out.println(num);
}

Each time through the loop, num is assigned a value from the array odds, in order.

When for each loop has iterated through all elements in the array, it continues on the next line after the loop (like when a standard for loop's termination condition is false).

Because the for each loop knows when it reaches the end of the array, it cannot cause an ArrayIndexOutOfBoundsException.

Practice Exercise

You must declare a local variable inside the for loop's parentheses. This means you cannot reuse a variable you have already declared.

// Legal
for (String s : stringArr){
  //...
}

// Illegal - compiler error
String s;
for (s : stringArr){
  //...
}

Drill

AdvancedForLoops/src/drills/ForEach.java * Use the code in each "forLoop" method to write a foreach loop in the corresponding "forEachLoop" method. Verify that the loop outputs are the same.

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