这篇文章主要介绍了Java如何实现HashMap排序的相关知识,内容详细易懂,操作简单快捷,具有一定借鉴价值,相信大家阅读完这篇Java如何实现HashMap排序文章都会有所收获,下面我们一起来看看吧。
使用stream进行排序(按key升序/降序)
package org.example.a; import java.util.*; public class Demo { public static void main(String[] args) { Map<String, String> map = new HashMap<>(); map.put("ad", "dd"); map.put("bc", "ee"); map.put("cb", "ff"); for (Map.Entry<String, String> entry : map.entrySet()) { System.out.println(entry.getKey() + ":" + entry.getValue()); } System.out.println(); Map<String, String> linkedHashMap = new LinkedHashMap<>(); // 默认按照升序排列 map.entrySet().stream().sorted(Map.Entry.comparingByKey()) .forEach(o -> linkedHashMap.put(o.getKey(), o.getValue())); for (Map.Entry<String, String> entry : linkedHashMap.entrySet()) { System.out.println(entry.getKey() + ":" + entry.getValue()); } System.out.println(); Map<String, String> linkedHashMap1 = new LinkedHashMap<>(); // 自定义排序(降序) map.entrySet().stream().sorted(Map.Entry.comparingByKey(new Comparator<String>() { @Override public int compare(String o1, String o2) { return o2.compareTo(o1); } })).forEach(o -> linkedHashMap1.put(o.getKey(), o.getValue())); for (Map.Entry<String, String> entry : linkedHashMap1.entrySet()) { System.out.println(entry.getKey() + ":" + entry.getValue()); } } }
执行结果
bc:ee
ad:dd
cb:ff
ad:dd
bc:ee
cb:ff
cb:ff
bc:ee
ad:dd
HashMap转TreeMap自定义排序(按key升序/降序)
package org.example.a; import java.util.Comparator; import java.util.HashMap; import java.util.Map; import java.util.TreeMap; public class Demo { public static void main(String[] args) { Map<String, String> map = new HashMap<>(); map.put("ad", "dd"); map.put("bc", "ee"); map.put("cb", "ff"); for (Map.Entry<String, String> entry : map.entrySet()) { System.out.println(entry.getKey() + ":" + entry.getValue()); } System.out.println(); // 默认按照升序排序 Map<String, String> map1 = new TreeMap<>(); map.forEach(map1::put); for (Map.Entry<String, String> entry : map1.entrySet()) { System.out.println(entry.getKey() + ":" + entry.getValue()); } System.out.println(); // 自定义排序(降序) Map<String, String> map2 = new TreeMap<>(new Comparator<String>() { @Override public int compare(String o1, String o2) { return o2.compareTo(o1); } }); map.forEach(map2::put); for (Map.Entry<String, String> entry : map2.entrySet()) { System.out.println(entry.getKey() + ":" + entry.getValue()); } } }
执行结果
bc:ee
ad:dd
cb:ff
ad:dd
bc:ee
cb:ff
cb:ff
bc:ee
ad:dd
使用stream进行排序(按value升序/降序)
package org.example.a; import java.util.*; public class Demo { public static void main(String[] args) { Map<String, String> map = new HashMap<>(); map.put("ad", "dd"); map.put("bc", "ee"); map.put("cb", "ff"); for (Map.Entry<String, String> entry : map.entrySet()) { System.out.println(entry.getKey() + ":" + entry.getValue()); } System.out.println(); Map<String, String> linkedHashMap = new LinkedHashMap<>(); // 默认按照升序排列 map.entrySet().stream().sorted(Map.Entry.comparingByValue()) .forEach(o -> linkedHashMap.put(o.getKey(), o.getValue())); for (Map.Entry<String, String> entry : linkedHashMap.entrySet()) { System.out.println(entry.getKey() + ":" + entry.getValue()); } System.out.println(); Map<String, String> linkedHashMap1 = new LinkedHashMap<>(); // 自定义排序(降序) map.entrySet().stream().sorted(Map.Entry.comparingByValue(new Comparator<String>() { @Override public int compare(String o1, String o2) { return o2.compareTo(o1); } })).forEach(o -> linkedHashMap1.put(o.getKey(), o.getValue())); for (Map.Entry<String, String> entry : linkedHashMap1.entrySet()) { System.out.println(entry.getKey() + ":" + entry.getValue()); } } }
执行结果
bc:ee
ad:dd
cb:ff
ad:dd
bc:ee
cb:ff
cb:ff
bc:ee
ad:dd
借助List进行排序(按value升序/降序)
原理:将待排序Map中的所有元素置于一个列表中,接着使用Collections的一个静态方法 sort(List<T> list, Comparator<? super T> c) 来排序列表,同样是用比较器定义比较规则。排序后的列表中的元素再依次装入Map,为了肯定的保证Map中元素与排序后的List中的元素的顺序一致,使用了LinkedHashMap数据类型。
本处只写升序代码,降序只是调换个顺序而已。
package org.example.a; import java.util.*; public class Demo { public static void main(String[] args) { Map<String, String> map = new HashMap<>(); map.put("ad", "dd"); map.put("bc", "ee"); map.put("cb", "ff"); for (Map.Entry<String, String> entry : map.entrySet()) { System.out.println(entry.getKey() + ":" + entry.getValue()); } System.out.println(); Map<String, String> sortedMap = new LinkedHashMap<>(); List<Map.Entry<String, String>> entryList = new ArrayList<Map.Entry<String, String>>( map.entrySet()); Collections.sort(entryList, new Comparator<Map.Entry<String, String>>() { @Override public int compare(Map.Entry<String, String> me1, Map.Entry<String, String> me2) { return me1.getValue().compareTo(me2.getValue()); } }); for (Map.Entry<String, String> stringStringEntry : entryList) { sortedMap.put(stringStringEntry.getKey(), stringStringEntry.getValue()); } for (Map.Entry<String, String> entry : sortedMap.entrySet()) { System.out.println(entry.getKey() + ":" + entry.getValue()); } } }
运行结果
bc:ee
ad:dd
cb:ff
ad:dd
bc:ee
cb:ff
package org.example.a; import java.util.*; public class Demo{ public static List arrayList = new ArrayList(); public static void main(String[] args) { Map<String, String> hashMap = new HashMap<String, String>(); hashMap.put("name1", "josan1"); hashMap.put("name2", "josan2"); hashMap.put("name3", "josan3"); Set<Map.Entry<String, String>> set = hashMap.entrySet(); Iterator<Map.Entry<String, String>> iterator = set.iterator(); while(iterator.hasNext()) { Map.Entry entry = iterator.next(); String key = (String) entry.getKey(); String value = (String) entry.getValue(); System.out.println("key:" + key + ", value:" + value); } } }
执行结果(未按照插入顺序输出)
key:name3, value:josan3
key:name2, value:josan2
key:name1, value:josan1
package org.example.a; import java.util.*; public class Demo{ public static List arrayList = new ArrayList(); public static void main(String[] args) { Map<String, String> hashMap = new LinkedHashMap<String, String>(); hashMap.put("name1", "josan1"); hashMap.put("name2", "josan2"); hashMap.put("name3", "josan3"); Set<Map.Entry<String, String>> set = hashMap.entrySet(); Iterator<Map.Entry<String, String>> iterator = set.iterator(); while(iterator.hasNext()) { Map.Entry entry = iterator.next(); String key = (String) entry.getKey(); String value = (String) entry.getValue(); System.out.println("key:" + key + ", value:" + value); } } }
执行结果(按照插入顺序输出)
key:name1, value:josan1
key:name2, value:josan2
key:name3, value:josan3
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