Java中for的几种常见形式
- For loop using index.
for (int i = 0; i < arr.length; i++) {
type var = arr[i];
body-of-loop
}
- Loop using explicit iterator.
for (Iterator<type> iter = coll.iterator(); iter.hasNext(); ) {
type var = iter.next();
body-of-loop
}
- Foreach loop over all elements in arr.
for (type var : coll) {
body-of-loop
}
For循环用来处理哪些数据结构
- 数组
int[] a = {1,2,3,4,5,6};
int[] b = new int[]{1,2,3,4,5,6};
int[] c = new int[6];
for (int i = 0; i < a.length; i++) {
System.out.println(i);
}
for (int i : a) {
System.out.println(i);
}
- 实现了java.util.Iterator的类
````aidl
import java.util.Iterator;
/**
* Created by MoXingwang on 2017/6/30.
*/
public class IterableTest<E> implements Iterable<E> {
public static void main(String[] args) {
IterableTest<Integer> integers = new IterableTest<Integer>();
for (Integer integer : integers) {
System.out.println(integer);
}
}
@Override
public Iterator<E> iterator() {
return new Iterator() {
@Override
public boolean hasNext() {
//...
return false;
}
@Override
public Object next() {
//...
return null;
}
@Override
public void remove() {
//...
}
};
}
}
普通for遍历和增强for的一些区别
增强的for循环的底层使用迭代器来实现，所以它就与普通for循环有一些差异
- 增强for使用增强for循环的时候不能使用集合删除集合中的元素；
- 增强for循环不能使用迭代器中的方法，例如remove()方法删除元素；
- 与普通for循环的区别：增强For循环有遍历对象，普通for循环没有遍历对象;
对于实现了RandomAccess接口的集合类，推荐使用普通for，这种方式faster than Iterator.next
The RandomAccess interface identifies that a particular java.util.List implementation has fast random access. (A more accurate name for the interface would have been "FastRandomAccess.") This interface tries to define an imprecise concept: what exactly is fast? The documentation provides a simple guide: if repeated access using the List.get( ) method is faster than repeated access using the Iterator.next( ) method, then the List has fast random access. The two types of access are shown in the following code examples.
