Java中的集合类HashMap的应用
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import java.util.Collections;import java.util.HashMap;import java.util.Iterator;import java.util.Set;/* * 产生50个10到50的随机数，用hashMap统计每个随机数出现的次数，并求这些随机数中的最大值和最小值 */public class Statistics{public static void main(String[] args){HashMap<Integer, Integer> hashMap = new HashMap<Integer, Integer>();for (int i = 0; i < 50; i++){//产生50个10到50的随机数int random=(int)Math.round(Math.random()*40+10);Integer key = Integer.valueOf(random);//使用hashMap统计每个随机数出现的次数，将随机数作为键，出现次数作为值if (hashMap.get(key) == null){hashMap.put(key, 1);} else {Integer value = (Integer)hashMap.get(key);value = Integer.valueOf(value.intValue() + 1);hashMap.put(key, value);}}Set<Integer> keyIntegers = (Set<Integer>)hashMap.keySet();for (Iterator<Integer> iterator = keyIntegers.iterator(); iterator.hasNext();){Integer keyInteger = (Integer)iterator.next();Integer valueInteger = (Integer)hashMap.get(keyInteger);System.out.println(keyInteger + "的出现次数是：" + valueInteger);}System.out.println("随机数中的最大值是：" + Collections.max(keyIntegers));System.out.println("随机数中的最小值是：" + Collections.min(keyIntegers));}} import java.util.HashMap;import java.util.Iterator;import java.util.Set;/** * HashMap的应用，统计一个字符串中同一字符出现的字数 * @author c */public class HashMapTest{public static void main(String[] args){String s = "ajlsdfjhlahfuirhgjdnfafidofj";char[] c = s.toCharArray();HashMap<Character, Integer> map = new HashMap<Character, Integer>();for (int i = 0; i < c.length; i++){/* * HaspMap的get方法如果不存在该键则返回null,如果存在则值（次数）加1 */if (map.get(Character.valueOf(c[i])) == null){map.put(Character.valueOf(c[i]), 1);} else {Integer value = map.get(Character.valueOf(c[i]));value = Integer.valueOf(value.intValue() + 1);map.put(Character.valueOf(c[i]), value);}}Set<Character> set = map.keySet();Iterator<Character> iterator = set.iterator();while (iterator.hasNext()){Character key = (Character)iterator.next();Integer val = (Integer)map.get(key);System.out.println("字符" + key + "的出现次数是：" + val);}}}
