Java为每个循环如何工作? [英] How does the Java 'for each' loop work?

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问题描述

考虑:

 列表< String> someList = new ArrayList< String>(); 
//向someList添加monkey,donkey,skeleton key





  for(String item:someList){
System.out.println(item);

$ / code>

相当于 c>循环看起来像不使用每个语法的

解决方案

  for(Iterator< String> i = someList.iterator(); i.hasNext();){
String item = i.next();
System.out.println(item);

$ / code>

请注意,如果您需要使用 i.remove (); 在你的循环中,或以某种方式访问​​实际的迭代器,你不能使用<:code>只是推断出来的。



正如Denis Bueno指出的,这段代码适用于任何实现 Iterable 界面

另外,如果(:)成语的右边是数组<$ code >而不是 Iterable 对象,内部代码使用一个int索引计数器,并相反检查 array.length 。请参阅 Java语言规范


Consider:

List<String> someList = new ArrayList<String>();
// add "monkey", "donkey", "skeleton key" to someList

for (String item : someList) {
    System.out.println(item);
}

What would the equivalent for loop look like without using the for each syntax?

解决方案

for (Iterator<String> i = someList.iterator(); i.hasNext();) {
    String item = i.next();
    System.out.println(item);
}

Note that if you need to use i.remove(); in your loop, or access the actual iterator in some way, you cannot use the for ( : ) idiom, since the actual iterator is merely inferred.

As was noted by Denis Bueno, this code works for any object that implements the Iterable interface.

Also, if the right-hand side of the for (:) idiom is an array rather than an Iterable object, the internal code uses an int index counter and checks against array.length instead. See the Java Language Specification.

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