Java SortedMap comparator()方法及示例

java.util.SortedMap 接口的 comparator() 方法用于返回用于对该地图中的键进行排序的比较器，如果该地图使用其键的自然排序，则为空。

语法：

public Comparator comparator()

返回值： 该方法返回用于对该地图中的键进行排序的 比较器 ，如果该地图使用其键的自然排序，则返回空。
下面的程序说明了comparator()方法：

例1： 用于自然排序。

// Java program to demonstrate
// comparator() method for natural ordering
 
import java.util.*;
 
public class GFG1 {
    public static void main(String[] argv)
        throws Exception
    {
 
        try {
 
            // Creating object of SortedTreeMap
            SortedMap<Integer, String>
                sotreemap = new TreeMap<Integer, String>();
 
            // Populating tree map
            sotreemap.put(1, "one");
            sotreemap.put(2, "two");
            sotreemap.put(3, "three");
            sotreemap.put(4, "four");
            sotreemap.put(5, "five");
 
            // Printing the SortedTreeMap
            System.out.println("SortedTreeMap: " + sotreemap);
 
            // Getting used Comparator in the map
            // using comparator() method
            Comparator comp = sotreemap.comparator();
 
            // Printing the comparator value
            System.out.println("Comparator value: "
                               + comp);
        }
 
        catch (NullPointerException e) {
            System.out.println("Exception thrown : " + e);
        }
    }
}

输出

SortedTreeMap: {1=one, 2=two, 3=three, 4=four, 5=five}
Comparator value: null

例2： 用于反向排序。

// Java program to demonstrate
// comparator() method
// for reverse ordering
 
import java.util.*;
 
public class GFG1 {
    public static void main(String[] argv)
        throws Exception<div class="code-output">
<b>Output:</b>
<pre>
Initial Mappings are: {10=Geeks, 15=4, 20=Geeks, 25=Welcomes, 30=You}
The set is: [10=Geeks, 15=4, 20=Geeks, 25=Welcomes, 30=You]
</pre>
</div>
 
    {
 
        try {
 
            // Creating object of TreeMap
            SortedMap<Integer, String>
                sotreemap = new TreeMap<Integer, String>(
                    Collections.reverseOrder());
 
            // Populating tree map
            sotreemap.put(1, "one");
            sotreemap.put(2, "two");
            sotreemap.put(3, "three");
            sotreemap.put(4, "four");
            sotreemap.put(5, "five");
 
            // Printing the TreeMap
            System.out.println("SortedTreeMap: " + sotreemap);
 
            // Getting used Comparator in the map
            // using comparator() method
            Comparator comp = sotreemap.comparator();
 
            // Printing the comparator value
            System.out.println("Comparator value: " + comp);
        }
 
        catch (NullPointerException e) {
            System.out.println("Exception thrown : " + e);
        }
    }
}

输出

SortedTreeMap: {5=five, 4=four, 3=three, 2=two, 1=one}
Comparator value: java.util.Collections$ReverseComparator@232204a1