Map遍历

import java.util.Map;import java.util.HashMap;import java.util.HashSet;import java.util.Iterator;import java.util.List;import java.util.Set;import java.util.Map.Entry;//增强For循环public class Main {public static void main(String[] args) {// 创建一个HashMap对象,并加入了一些键值对。Map<String, String> maps = new HashMap<String, String>();maps.put("1", "PHP");maps.put("2", "Java");maps.put("3", "C");maps.put("4", "C++");maps.put("5", "HTML");// 传统的遍历map集合的方法1; keySet()//traditionalMethod1(maps);// 传统的遍历map集合的方法2; entrySet()//traditionalMethod2(maps);// 使用增强For循环来遍历map集合方法1; keySet()//strongForMethod1(maps);// 使用增强For循环来遍历map集合方法2; entrySet()strongForMethod2(maps);}private static void strongForMethod2(Map<String, String> maps) {Set<Entry<String, String>> set = maps.entrySet();for (Entry<String, String> entry : set) {String key = entry.getKey();String value = entry.getValue();System.out.println(key + " : " + value);}}private static void strongForMethod1(Map<String, String> maps) {Set<String> set = maps.keySet();for (String s : set) {String key = s;String value = maps.get(s);System.out.println(key + " : " + value);}}// 使用entrySet()方法，获取maps集合中的每一个键值对，private static void traditionalMethod2(Map<String, String> maps) {Set<Map.Entry<String, String>> sets = maps.entrySet();// 取得迭代器遍历出对应的值。Iterator<Entry<String, String>> it = sets.iterator();while (it.hasNext()) {Map.Entry<String, String> entry = (Entry<String, String>) it.next();String key = entry.getKey();String value = entry.getValue();System.out.println(key + " : " + value);}}// 使用keySet()方法，获取maps集合中的所有键，遍历键取得所对应的值。private static void traditionalMethod1(Map<String, String> maps) {Set<String> sets = maps.keySet();// 取得迭代器遍历出对应的值Iterator<String> it = sets.iterator();while (it.hasNext()) {String key = it.next();String value = maps.get(key);System.out.println(key + " : " + value);}}}

以上代码运行输出结果为：

1 : PHP2 : Java3 : C4 : C++5 : HTML

根据 key从map 里取出元素，并转成 Long、Integer

Long value1 = MapUtils.getLong(map, key);Integer value2 = MapUtils.getInteger(map, key);

这样取出数据能够实现先判空，再判断类型，之后转换，防止报错。

内部实现：

public static Long getLong(final Map map, final Object key) {Number answer = getNumber(map, key);if (answer == null) {return null;} else if (answer instanceof Long) {return (Long) answer;}return new Long(answer.longValue());}

集合反转（List反向输出）

import java.util.ArrayList;import java.util.Collections;import java.util.List;import java.util.ListIterator;class Main {public static void main(String[] args) {String[] coins = { "A", "B", "C", "D", "E" };List l = new ArrayList();for (int i = 0; i < coins.length; i++)l.add(coins[i]);ListIterator liter = l.listIterator();System.out.println("反转前");while (liter.hasNext())System.out.println(liter.next());Collections.reverse(l);liter = l.listIterator();System.out.println("反转后");while (liter.hasNext())System.out.println(liter.next());}}

以上代码运行输出结果为：

反转前ABCDE反转后EDCBA

删除集合中指定元素（Set删除指定元素）

import java.util.*;public class Main {public static void main(String [] args) { System.out.println( "集合实例!\n" ); int size;HashSet collection = new HashSet ();String str1 = "Yellow", str2 = "White", str3 = "Green", str4 = "Blue"; Iterator iterator;collection.add(str1); collection.add(str2); collection.add(str3); collection.add(str4);System.out.print("集合数据: "); iterator = collection.iterator();while (iterator.hasNext()){System.out.print(iterator.next() + " "); }System.out.println();collection.remove(str2);System.out.println("删除之后 [" + str2 + "]\n");System.out.print("现在集合的数据是: ");iterator = collection.iterator();while (iterator.hasNext()){System.out.print(iterator.next() + " "); }System.out.println();size = collection.size();System.out.println("集合大小: " + size + "\n");}}

以上代码运行输出结果为：

集合实例!集合数据: White Yellow Blue Green 删除之后 [White]现在集合的数据是: Yellow Blue Green 集合大小: 3

只读集合

import java.util.ArrayList;import java.util.Arrays;import java.util.Collections;import java.util.HashMap;import java.util.HashSet;import java.util.List;import java.util.Map;import java.util.Set;public class Main {public static void main(String[] argv) throws Exception {List stuff = Arrays.asList(new String[] { "a", "b" });List list = new ArrayList(stuff);list = Collections.unmodifiableList(list);try {list.set(0, "new value");} catch (UnsupportedOperationException e) {}Set set = new HashSet(stuff);set = Collections.unmodifiableSet(set);Map map = new HashMap();map = Collections.unmodifiableMap(map);System.out.println("集合现在是只读");}}

以上代码运行输出结果为：

集合现在是只读

集合输出（TreeMap操作）

import java.util.*;public class Main{public static void main(String[] args) {System.out.println("TreeMap 实例！\n");TreeMap tMap = new TreeMap();tMap.put(1, "Sunday");tMap.put(2, "Monday");tMap.put(3, "Tuesday");tMap.put(4, "Wednesday");tMap.put(5, "Thursday");tMap.put(6, "Friday");tMap.put(7, "Saturday");System.out.println("TreeMap 键：" + tMap.keySet());System.out.println("TreeMap 值：" + tMap.values());System.out.println("键为 5 的值为: " + tMap.get(5)+ "\n");System.out.println("第一个键: " + tMap.firstKey() + " Value: " + tMap.get(tMap.firstKey()) + "\n");System.out.println("最后一个键: " + tMap.lastKey() + " Value: "+ tMap.get(tMap.lastKey()) + "\n");System.out.println("移除第一个数据: " + tMap.remove(tMap.firstKey()));System.out.println("现在 TreeMap 键为: " + tMap.keySet());System.out.println("现在 TreeMap 包含: " + tMap.values() + "\n");System.out.println("移除最后一个数据: " + tMap.remove(tMap.lastKey()));System.out.println("现在 TreeMap 键为: " + tMap.keySet());System.out.println("现在 TreeMap 包含: " + tMap.values());}}

以上代码运行输出结果为：

TreeMap 实例！TreeMap 键：[1, 2, 3, 4, 5, 6, 7]TreeMap 值：[Sunday, Monday, Tuesday, Wednesday, Thursday, Friday, Saturday]键为 5 的值为: Thursday第一个键: 1 Value: Sunday最后一个键: 7 Value: Saturday移除第一个数据: Sunday现在 TreeMap 键为: [2, 3, 4, 5, 6, 7]现在 TreeMap 包含: [Monday, Tuesday, Wednesday, Thursday, Friday, Saturday]移除最后一个数据: Saturday现在 TreeMap 键为: [2, 3, 4, 5, 6]现在 TreeMap 包含: [Monday, Tuesday, Wednesday, Thursday, Friday]

集合转数组（List转Array）

import java.util.*;public class Main{public static void main(String[] args){List<String> list = new ArrayList<String>();list.add("我"); list.add("的"); list.add("天");list.add("堂");list.add("");String[] s1 = list.toArray(new String[0]); for(int i = 0; i < s1.length; ++i){String contents = s1[i];System.out.print(contents);} }}

以上代码运行输出结果为：

我的天堂

List 循环移动元素

以下实例演示了如何使用 Collections 类的 rotate() 来循环移动元素，方法第二个参数指定了移动的起始位置：

import java.util.*;public class Main {public static void main(String[] args) {List list = Arrays.asList("one Two three Four five six".split(" "));System.out.println("List :"+list);Collections.rotate(list, 3);System.out.println("rotate: " + list);}}

以上代码运行输出结果为：

List :[one, Two, three, Four, five, six]rotate: [Four, five, six, one, Two, three]

Java 集合List Set HashMap操作二（Map遍历 List反向 Set删除指定元素 集合只读 TreeMap操作 List转Array List移动元素）