Iterate without an index
Ways of iterating
Modernize old code
for-each
loop is used with both collections and arrays. It's intended to simplify
the most common form of iteration, where the iterator or index is used
solely for iteration, and not for any other kind of operation, such as
removing or editing an item in the collection or array. When there is a
choice, the for-each
loop should be preferred over the for
loop, since it increases legibility.
Example
Here are some examples of the for-each
loop.
import java.util.*; import java.math.BigDecimal; public final class ForEachExamples { public static void main(String... args){ List<Number> numbers = new ArrayList<>(); numbers.add(42); numbers.add(-30); numbers.add(new BigDecimal("654.2")); //typical for-each loop //processes each item, without changing the collection or array. for (Number number : numbers){ log(number); } //use with an array String[] names = {"Ethan Hawke", "Julie Delpy"}; for(String name : names){ log("Name : " + name); } //removal of items requires an explicit iterator, //so you can't use a for-each loop in this case Collection<String> words = new ArrayList<>(); words.add("Il ne lui faut que deux choses: "); words.add("le"); words.add("pain"); words.add("et"); words.add("le"); words.add("temps."); words.add("- Alfred de Vigny."); for(Iterator<String> iter = words.iterator(); iter.hasNext();){ if (iter.next().length() == 4){ iter.remove(); } } log("Edited words: " + words.toString()); //if used with a non-parameterized type (not recommended!), //then Object must be used, along with a cast Collection stuff = new ArrayList(); stuff.add("blah"); for (Object thing : stuff){ String item = (String)thing; log("Thing : " + item); } } // PRIVATE private static void log(Object aThing){ System.out.println(aThing); } }