| 知乎专栏 |
Iterator接口包含四个方法：hasNext，next，remove，forEachRemaining
package cn.netkiller.test;
import java.util.Iterator;
import java.util.List;
public class Test {
public static void main(String[] args) {
Test test = new Test();
// ArrayList<String> arrayList = new ArrayList<String>();
List<String> list = List.of("Neo", "Tom", "Jerry");
System.out.printf("%s for %s\n", "=".repeat(10), "=".repeat(10));
for (String name : list) {
System.out.println(name);
}
System.out.printf("%s forEach %s\n", "=".repeat(10), "=".repeat(10));
list.forEach(obj -> {
System.out.println(obj);
});
Iterator<String> iterator = list.iterator();
System.out.printf("%s while %s\n", "=".repeat(10), "=".repeat(10));
while (iterator.hasNext()) {
System.out.println(iterator.next());
}
System.out.printf("%s forEachRemaining %s\n", "=".repeat(10), "=".repeat(10));
iterator.forEachRemaining(System.out::println);
}
}
package cn.netkiller.test;
import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;
public class Test {
public static void main(String[] args) {
System.out.printf("%s Map<Integer, String> %s\n", "=".repeat(10), "=".repeat(10));
Map<Integer, String> map = new HashMap<Integer, String>();
for (int i = 0; i < 10; i++) {
map.put(i, "map" + i);
}
Iterator iterMap = map.entrySet().iterator();
while (iterMap.hasNext()) {
Map.Entry strMap = (Map.Entry) iterMap.next();
System.out.println("key: " + strMap.getKey() + ", value: " + strMap.getValue());
}
}
}
List 加载后放入内存，可以可以反复使用，Iterator 一旦调用 next() 就会从内存中清除，无法再次引用。
package cn.netkiller.test;
import java.util.Iterator;
import java.util.List;
public class Test {
public static void main(String[] args) {
List<String> list = List.of("Neo", "Tom", "Jerry");
System.out.printf("%s List<String> %s\n", "=".repeat(10), "=".repeat(10));
list.forEach(System.out::println);
Iterator<String> iterator = list.iterator();
System.out.printf("%s next() %s\n", "=".repeat(10), "=".repeat(10));
String name = iterator.next();
System.out.println(name);
System.out.printf("%s forEachRemaining() %s\n", "=".repeat(10), "=".repeat(10));
iterator.forEachRemaining(System.out::println);
System.out.printf("%s while hasNext() %s\n", "=".repeat(10), "=".repeat(10));
while (iterator.hasNext()) {
System.out.println(iterator.next());
}
}
}
输出结果
========== List<String> ========== Neo Tom Jerry ========== next() ========== Neo ========== forEachRemaining() ========== Tom Jerry ========== while hasNext() ==========
package cn.netkiller.test;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;
public class Test {
public static void main(String[] args) {
List<String> list = new ArrayList<>(List.of("Neo", "Tom", "Jerry"));
System.out.printf("%s List<String> %s\n", "=".repeat(10), "=".repeat(10));
list.forEach(System.out::println);
Iterator<String> iterator = list.iterator();
System.out.printf("%s remove() %s\n", "=".repeat(10), "=".repeat(10));
while (iterator.hasNext()) {
String name = iterator.next();
if (name.equals("Tom")) {
iterator.remove();
} else {
System.out.println(name);
}
}
}
}
UnsupportedOperationException 异常
Exception in thread "main" java.lang.UnsupportedOperationException at java.base/java.util.ImmutableCollections.uoe(ImmutableCollections.java:142) at java.base/java.util.ImmutableCollections$ListItr.remove(ImmutableCollections.java:387) at cn.netkiller.test.Test.main(Test.java:36)
List.of 跟 Arrays.asList 不支持 remove() 操作，会抛出 UnsupportedOperationException 异常。
List<String> list = List.of("Neo", "Tom", "Jerry");
List<String> list = Arrays.asList("Neo", "Tom", "Jerry");
Iterable<Entity> iterable = repository.findAll();
List<Entity> list = new ArrayList<>();
iterable.forEach(single->{list.add(single);});
List<String> result = new ArrayList<String>();
iterable.forEach(result::add);
List<String> result = new ArrayList<String>();
for (String str : iterable) {
result.add(str);
}
List<String> result = new ArrayList<String>();
while (iterator.hasNext()) {
result.add(iterator.next());
}
List<String> result = StreamSupport.stream(iterable.spliterator(), false).collect(Collectors.toList());
List<String> result = StreamSupport.stream(Spliterators.spliteratorUnknownSize(iterator, Spliterator.ORDERED), false).collect(Collectors.toList());
List<String> result = new ArrayList<String>();
iterator.forEachRemaining(result::add);
ListIterator 可以实现添加/删除和向前/向后访问数据
Iterator 可以用于 List / Set / Vector / Map 数据结构，ListIterator 只能用于 List
package cn.netkiller.test;
import java.util.ArrayList;
import java.util.LinkedList;
import java.util.List;
import java.util.ListIterator;
public class Test {
public static void main(String[] args) {
Test test = new Test();
List<String> arrayList = new ArrayList<String>();
List<String> linkedList = new LinkedList<String>();
linkedList.add("Neo");
linkedList.add("Tom");
linkedList.add("Jerry");
ListIterator<String> listIterator = linkedList.listIterator();
String first = listIterator.next();
System.out.printf("%s List<String> %s\n", "=".repeat(10), "=".repeat(10));
System.out.println("first:" + first);
listIterator.remove();
System.out.printf("%s forEachRemaining %s\n", "=".repeat(10), "=".repeat(10));
listIterator.add("Netkiller");
listIterator.forEachRemaining(System.out::println);
arrayList.add("Netkiller Linux 手札");
arrayList.add("Netkiller Java 手札");
arrayList.add("Netkiller Sprint 手札");
listIterator = arrayList.listIterator();
System.out.printf("%s next() %s\n", "=".repeat(10), "=".repeat(10));
while (listIterator.hasNext()) {
System.out.println(listIterator.next());
}
listIterator.add("Netkiller MySQL 手札");
System.out.printf("%s previous() %s\n", "=".repeat(10), "=".repeat(10));
while (listIterator.hasPrevious()) {
System.out.println(listIterator.previous());
}
}
}
String next = listIterator.next();
if( "Neo".equals(next)) {
listIterator.set("Netkiller");
}
List<String> items = new ArrayList<String>(); String nextWithIndex = items.get(listIterator.nextIndex()); String previousWithIndex = items.get(listIterator.previousIndex());
在 Java 中，Iterable接口是所有可迭代集合（如List、Set等）的父接口，其核心方法iterator()返回一个Iterator对象，用于遍历集合元素。
Iterable<String> iterable = Arrays.asList("a", "b", "c");
// for-each循环直接遍历元素
for (String element : iterable) {
System.out.println(element); // 输出：a、b、c
}
Iterable<Integer> numbers = Arrays.asList(1, 2, 3, 4);
Iterator<Integer> iterator = numbers.iterator();
// 循环判断是否有下一个元素
while (iterator.hasNext()) {
Integer num = iterator.next(); // 获取下一个元素
System.out.println(num);
// 示例：删除偶数（仅支持可修改的集合，如ArrayList，不可修改集合会抛异常）
if (num % 2 == 0) {
iterator.remove(); // 必须在next()之后调用，否则报错
}
}
对于支持流式操作的Iterable（如集合类），可通过stream()或parallelStream()转换为流，结合 Lambda 表达式实现函数式遍历：
Iterable<String> words = Arrays.asList("apple", "banana", "cherry");
// 转换为流并遍历
words.forEach(word -> System.out.println(word.toUpperCase())); // 输出大写字母
// 更复杂的流操作（过滤、映射等）
((Collection<String>) words).stream() // 注意：需强转为Collection才能调用stream()
.filter(word -> word.length() > 5)
.forEach(System.out::println); // 输出：banana、cherry
遍历自定义 Iterable 对象，若你自定义了实现Iterable接口的类，只需重写iterator()方法，即可使用上述所有遍历方式：
public class MyIterable implements Iterable<String> {
private String[] data = {"x", "y", "z"};
@Override
public Iterator<String> iterator() {
return new Iterator<String>() {
private int index = 0;
@Override
public boolean hasNext() {
return index < data.length;
}
@Override
public String next() {
if (!hasNext()) {
throw new NoSuchElementException();
}
return data[index++];
}
};
}
// 测试遍历
public static void main(String[] args) {
MyIterable myIterable = new MyIterable();
for (String s : myIterable) {
System.out.println(s); // 输出：x、y、z
}
}
}