java.util.SortedMap接口的comparator()方法用于返回用于对该映射中的键进行排序的比较器；如果此映射使用其键的自然顺序，则返回null。

用法:

public Comparator comparator()

返回值：此方法返回用于对该映射中的键进行排序的比较器；如果此映射使用其键的自然顺序，则返回null。

以下示例程序旨在说明comparator()方法：

范例1：对于自然排序。

// 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

sotreemap = new TreeMap();

// Populating tree map

sotreemap.put(1, "one");

sotreemap.put(2, "two");

sotreemap.put(3, "three");

sotreemap.put(4, "four");

sotreemap.put(5, "five");

// Pritnig the SortedTreeMap

System.out.println("SortedTreeMap:" + sotreemap);

// Getting used Comparator in the map

// using comparator() method

Comparator comp = sotreemap.comparator();

// Pritnig 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

范例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

{

try {

// Creating object of TreeMap

SortedMap

sotreemap = new TreeMap(

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");

// Pritnig the TreeMap

System.out.println("SortedTreeMap:" + sotreemap);

// Getting used Comparator in the map

// using comparator() method

Comparator comp = sotreemap.comparator();

// Pritnig 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