The enhanced for-loop is a popular feature introduced with the Java SE platform in version 5.0. Its simple structure allows one to simplify code by presenting for-loops that visit each element of an array\/collection without explicitly expressing how one goes from element to element. <\/P>
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Because the old style of coding didn’t become invalid with the new for-loop syntax, you don’t have to use an enhanced for-loop when visiting each element of an array\/collection. However, with the new style, one’s code would typically change from something like the following: <\/P>
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Assuming “array” is defined to be an array of If you have a class called You cannot just pass an In order to be able to use your class with an enhanced for-loop, it does need an Actually, to be more correct, you can use a generic It is this By adding the proper implements clause:<\/P> Keep in mind that the individual penguins are internally kept in a Set type collection so the returned order doesn’t necessarily match the insertion order, which in this case it doesn’t. <\/P> Remember to genericize the implements clause for the class “ For more information on the enhanced for-loop, please see the Java Programming Language guide from JDK 1.5<\/A>.<\/P> The enhanced for-loop is a popular feature introduced with the Java SE platform in version 5.0. Its simple structure allows one to simplify code by presenting for-loops that visit each element of an array\/collection without explicitly expressing how one goes from element to element. Because the old style of coding didn’t become invalid with the … Continue reading Using Enhanced For-Loops with Your Classes<\/span><\/a><\/p>\n","protected":false},"author":2,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[],"tags":[],"class_list":["post-223","post","type-post","status-publish","format-standard","hentry"],"_links":{"self":[{"href":"https:\/\/www.strongd.net\/index.php?rest_route=\/wp\/v2\/posts\/223","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.strongd.net\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.strongd.net\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.strongd.net\/index.php?rest_route=\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/www.strongd.net\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=223"}],"version-history":[{"count":0,"href":"https:\/\/www.strongd.net\/index.php?rest_route=\/wp\/v2\/posts\/223\/revisions"}],"wp:attachment":[{"href":"https:\/\/www.strongd.net\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=223"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.strongd.net\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=223"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.strongd.net\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=223"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}for (int i=0; i<array.length; i++) {<\/CODE> System.out.println(“Element: ” + array[i]);<\/CODE>}<\/CODE>to the newer form:<\/CODE>for (String element : array) {<\/CODE> System.out.println(“Element: ” + element);<\/CODE>}<\/CODE>
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\nString<\/CODE> objects, each element is assigned to the element variable as it loops through the array. These basics of the enhanced for-loop were covered in an earlier Tech Tip: The Enhanced For Loop<\/A>, from May 5, 2005.<\/P>
\nColony<\/CODE> which contains a group of Penguin<\/CODE> objects, without doing anything extra to get the enhanced for-loop to work, one way you would loop through each penguin element would be to return an Iterator<\/CODE> and iterate through the colony. Unfortunately, the enhanced for-loop does not work with Iterator<\/CODE> , so the following won’t even compile: <\/P>\/\/ Does not compile<\/CODE>import java.util.*;<\/CODE>public class BadColony {<\/CODE> static class Penguin {<\/CODE> String name;<\/CODE> Penguin(String name) {<\/CODE> this.name = name;<\/CODE> }<\/CODE> public String toString() {<\/CODE> return “Penguin{” + name + “}”;<\/CODE> }<\/CODE> }<\/CODE> Set<Penguin> set = new HashSet<Penguin>();<\/CODE> public void addPenguin(Penguin p) {<\/CODE> set.add(p);<\/CODE> }<\/CODE> public Iterator<Penguin> getPenguins() {<\/CODE> return set.iterator();<\/CODE> }<\/CODE> public static void main(String args[]) {<\/CODE> Colony colony = new Colony();<\/CODE> Penguin opus = new Penguin(“Opus”);<\/CODE> Penguin chilly = new Penguin(“Chilly Willy”);<\/CODE> Penguin mumble = new Penguin(“Mumble”);<\/CODE> Penguin emperor = new Penguin(“Emperor”);<\/CODE> colony.addPenguin(opus);<\/CODE> colony.addPenguin(chilly);<\/CODE> colony.addPenguin(mumble);<\/CODE> colony.addPenguin(emperor);<\/CODE> Iterator<Penguin> it = colony.getPenguins();<\/CODE>\/\/ The bad line of code:<\/CODE> for (Penguin p : it) {<\/CODE> System.out.println(p);<\/CODE> }<\/CODE> }<\/CODE>}<\/CODE>
\nIterator<\/CODE> into the enhanced for-loop. The 2nd line of the following will generate a compilation error: <\/P> Iterator<Penguin> it = colony.getPenguins();<\/CODE> for (Penguin p : it) {<\/CODE>
The error:BadColony.java:36: foreach not applicable to expression type<\/CODE> for (Penguin p : it) {<\/CODE> ^<\/CODE>1 error<\/CODE>
\nIterator<\/CODE> , but that Iterator<\/CODE> must be provided via the Iterable<\/CODE> interface: <\/P>public interface java.lang.Iterable {<\/CODE> public java.util.Iterator iterator();<\/CODE>}<\/CODE>
\nT<\/CODE> , allowing the enhanced for-loop to avoid casting, returning the designated generic type, instead of just a plain old Object<\/CODE> . <\/P>public interface java.lang.Iterable<T> {<\/CODE> public java.util.Iterator<T> iterator();<\/CODE>}<\/CODE>
\nIterable<\/CODE> object which is then provided to the enhanced for-loop. By making the Colony<\/CODE> class implement Iterable<\/CODE> , and having its new iterator()<\/CODE> method return the Iterator<\/CODE> that getPenguins()<\/CODE> provides, you’ll be able to loop through the penguins in the colony via an enhanced for-loop. <\/P>
\npublic class Colony implements Iterable<Colony.Penguin> {<\/CODE>
You then get your enhanced for-loop for the colony: for (Penguin p : colony) {<\/CODE>
Here’s the updated Colony<\/CODE> class with the corrected code:import java.util.*;<\/CODE>public class Colony implements Iterable<Colony.Penguin> {<\/CODE> static class Penguin {<\/CODE> String name;<\/CODE> Penguin(String name) {<\/CODE> this.name = name;<\/CODE> }<\/CODE> public String toString() {<\/CODE> return “Penguin{” + name + “}”;<\/CODE> }<\/CODE> }<\/CODE> Set<Penguin> set = new HashSet<Penguin>();<\/CODE> public void addPenguin(Penguin p) {<\/CODE> set.add(p);<\/CODE> }<\/CODE> public Iterator<Penguin> getPenguins() {<\/CODE> return set.iterator();<\/CODE> }<\/CODE> public Iterator<Penguin> iterator() {<\/CODE> return getPenguins();<\/CODE> }<\/CODE> public static void main(String args[]) {<\/CODE> Colony colony = new Colony();<\/CODE> Penguin opus = new Penguin(“Opus”);<\/CODE> Penguin chilly = new Penguin(“Chilly Willy”);<\/CODE> Penguin mumble = new Penguin(“Mumble”);<\/CODE> Penguin emperor = new Penguin(“Emperor”);<\/CODE> colony.addPenguin(opus);<\/CODE> colony.addPenguin(chilly);<\/CODE> colony.addPenguin(mumble);<\/CODE> colony.addPenguin(emperor);<\/CODE> for (Penguin p : colony) {<\/CODE> System.out.println(p);<\/CODE> }<\/CODE> }<\/CODE>}<\/CODE>
Running the code produces the following output: > java Colony<\/CODE> Penguin{Chilly Willy}<\/CODE> Penguin{Mumble}<\/CODE> Penguin{Opus}<\/CODE> Penguin{Emperor}<\/CODE>
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\nimplements Iterable<T><\/CODE> ” and not just say “implements Iterable<\/CODE> “. With the latter, the enhanced for-loop will only return an Object<\/CODE> for each element. <\/P>
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