Sort a Map by values (Java) HashMap按value值排序

   <span style="font-size:18px;">  对HashMap按value值的大小进行排序，方法如下。</span>

import java.util.*;public class MapUtil{    public static <K, V extends Comparable<? super V>> Map<K, V>         sortByValue( Map<K, V> map )    {        List<Map.Entry<K, V>> list =            new LinkedList<Map.Entry<K, V>>( map.entrySet() );        Collections.sort( list, new Comparator<Map.Entry<K, V>>()        {            public int compare( Map.Entry<K, V> o1, Map.Entry<K, V> o2 )            {                return (o1.getValue()).compareTo( o2.getValue() );            }        } );        Map<K, V> result = new LinkedHashMap<K, V>();        for (Map.Entry<K, V> entry : list)        {            result.put( entry.getKey(), entry.getValue() );        }        return result;    }}

And an associated JUnit4 test so you don't have to take my word for it:

import java.util.*;
import org.junit.*;

public class MapUtilTest
{
    @Test
    public void testSortByValue()
    {
        Random random = new Random(System.currentTimeMillis());
        Map<String, Integer> testMap = new HashMap<String, Integer>(1000);
        for(int i = 0 ; i < 1000 ; ++i) {
            testMap.put( "SomeString" + random.nextInt(), random.nextInt());
        }

        testMap = MapUtil.sortByValue( testMap );
        Assert.assertEquals( 1000, testMap.size() );

        Integer previous = null;
        for(Map.Entry<String, Integer> entry : testMap.entrySet()) {
            Assert.assertNotNull( entry.getValue() );
            if (previous != null) {
                Assert.assertTrue( entry.getValue() >= previous );
            }
            previous = entry.getValue();
        }
    }

}

Java 7 Version:

public static <K, V extends Comparable<? super V>> Map<K, V> 
    sortByValue( Map<K, V> map )
{
    List<Map.Entry<K, V>> list =
        new LinkedList<>( map.entrySet() );
    Collections.sort( list, new Comparator<Map.Entry<K, V>>()
    {
        @Override
        public int compare( Map.Entry<K, V> o1, Map.Entry<K, V> o2 )
        {
            return ( o1.getValue() ).compareTo( o2.getValue() );
        }
    } );

    Map<K, V> result = new LinkedHashMap<>();
    for (Map.Entry<K, V> entry : list)
    {
        result.put( entry.getKey(), entry.getValue() );
    }
    return result;
}

Java 8 Version:

public static <K, V extends Comparable<? super V>> Map<K, V> 
    sortByValue( Map<K, V> map )
{
    Map<K, V> result = new LinkedHashMap<>();
    Stream<Map.Entry<K, V>> st = map.entrySet().stream();

    st.sorted( Map.Entry.comparingByValue() )
        .forEachOrdered( e -> result.put(e.getKey(), e.getValue()) );

    return result;
}

在JAVA8版本中，

st.sorted(Map.Entry.comparingByValue()).forEachOrdered(e->result.put(e.getKey(), e.getValue()));

也可写成：

 st.sorted(Comparator.comparing(e -> e.getValue())).forEach(e -> result.put(e.getKey(), e.getValue()));

以上是按照升序排序的，按照降序排序方法如下：

import java.util.*;
import java.util.stream.Stream;

public class MapUtil {

public static <K, V extends Comparable<? super V>> Map<K, V> sortByValue( Map<K, V> map) {
    Map<K, V> result = new LinkedHashMap<>();
    Stream<Map.Entry<K, V>> st = map.entrySet().stream();

    Comparator ok = new Comparator<Map.Entry<K, V>>()
        {
            public int compare( Map.Entry<K, V> o1, Map.Entry<K, V> o2 )
            {
                return (o2.getValue()).compareTo( o1.getValue() );
            }
        };

    st.sorted(ok).forEachOrdered(e->result.put(e.getKey(), e.getValue()));
    return result;
}
}