Map接口方法和遍历方式

Map接口的常用方法

• put()：添加

• remove()：根据键删除映射关系

• get()：根据键获取值

• size()：获取元素个数

• isEmpty()：判断个数是否为零

• clear()：清除

• containsKey()：查找键是否存在

Map接口的六大遍历方式

• keySet()：获取所有的键

• values()：获取所有的值

• entrySet()：获取所有的关系k-v

第一组：先取出所有的Key，通过Key取出对应的Value

• 使用增强for循环

public class Demo02 {public static void main(String[] args) {Map map = new HashMap();map.put("邓超","孙俪");map.put("王宝强","马蓉");map.put("宋喆","马蓉");map.put("刘令博","null");map.put("null","刘亦菲");map.put("鹿晗","关晓彤");
​Set keyset = map.keySet();for (Object key : keyset) {System.out.println(key+"-"+map.get(key));}}
}

• 使用迭代器

public class Demo02 {public static void main(String[] args) {Map map = new HashMap();map.put("邓超","孙俪");map.put("王宝强","马蓉");map.put("宋喆","马蓉");map.put("刘令博","null");map.put("null","刘亦菲");map.put("鹿晗","关晓彤");Set keyset = map.keySet();Iterator iterator = keyset.iterator();while (iterator.hasNext()) {Object key =  iterator.next();System.out.println(key+"-"+map.get(key));}}
}
​

第二组：把所有的values取出

• 使用增强for循环

public class Demo02 {public static void main(String[] args) {Map map = new HashMap();map.put("邓超","孙俪");map.put("王宝强","马蓉");map.put("宋喆","马蓉");map.put("刘令博","null");map.put("null","刘亦菲");map.put("鹿晗","关晓彤");Collection values = map.values();for (Object value : values) {System.out.println(value);}}
}

• 使用迭代器

public class Demo02 {public static void main(String[] args) {Map map = new HashMap();map.put("邓超","孙俪");map.put("王宝强","马蓉");map.put("宋喆","马蓉");map.put("刘令博","null");map.put("null","刘亦菲");map.put("鹿晗","关晓彤");Iterator iterator2 = values.iterator();while (iterator2.hasNext()) {Object value =  iterator2.next();System.out.println(value);}}
}
​

第三组：通过EntrySet 来获取 k-v

• 使用增强for循环

public class Demo02 {public static void main(String[] args) {Map map = new HashMap();map.put("邓超","孙俪");map.put("王宝强","马蓉");map.put("宋喆","马蓉");map.put("刘令博","null");map.put("null","刘亦菲");map.put("鹿晗","关晓彤");Set entrySet = map.entrySet();for (Object entry : entrySet) {Map.Entry m = (Map.Entry) entry;System.out.println(m.getKey()+"-"+m.getValue());}}
}

• 使用迭代器

public class Demo02 {public static void main(String[] args) {Map map = new HashMap();map.put("邓超","孙俪");map.put("王宝强","马蓉");map.put("宋喆","马蓉");map.put("刘令博","null");map.put("null","刘亦菲");map.put("鹿晗","关晓彤");Set entrySet = map.entrySet();Iterator iterator = entrySet.iterator();while (iterator.hasNext()) {Object entry =  iterator.next();Map.Entry m = (Map.Entry)entry;System.out.println(m.getKey()+"-"+m.getValue());}}
}

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