Java 中的 TreeMap 比较器()方法，带示例
原文:https://www . geesforgeks . org/tree map-comparator-in-Java-method-with-examples/
Java . util . treemap类的比较器()方法用于返回用于排序此地图中的键的比较器，如果此地图使用其键的自然排序，则返回 null。
--> java.util Package
--> TreeMap Class
--> comparator() Method
语法:
public Comparator comparator()
返回类型:该方法返回用于对该地图中的关键点进行排序的比较器，如果该地图使用其关键点的自然排序，则返回 null。
注: 下行方式默认为自然排序。
例 1: 自然排序
Java 语言(一种计算机语言，尤用于创建网站)
// Java program to Illustrate comparator() Method
// for Natural Ordering (Descending Order)
// Importing required classes
import java.util.*;
// Main class
public class GFG {
// Main driver method
public static void main(String[] argv) throws Exception
{
// Try block to check for exceptions
try {
// Creating an empty TreeMap by
// creating object of NavigableMap
NavigableMap<Integer, String> treemap
= new TreeMap<Integer, String>();
// Populating TreeMap
// using put() method
treemap.put(1, "one");
treemap.put(2, "two");
treemap.put(3, "three");
treemap.put(4, "four");
treemap.put(5, "five");
// Printing the TreeMap
System.out.println("TreeMap: " + treemap);
// Getting used Comparator in the map
// using comparator() method
Comparator comp = treemap.comparator();
// Printing the comparator value
System.out.println("Comparator value: " + comp);
}
// Catch block to handle the exception
catch (NullPointerException e) {
// Display message if exception occurs
System.out.println("Exception thrown : " + e);
}
}
}
Output:
TreeMap: {1=one, 2=two, 3=three, 4=four, 5=five}
Comparator value: null
示例 2: 用于反向排序
Java 语言(一种计算机语言，尤用于创建网站)
// Java program to demonstrate comparator() Method
// for Reverse Ordering
// Importing required classes
import java.util.*;
// Main class
public class GFG {
// Main driver method
public static void main(String[] argv) throws Exception
{
// Try block to check for exceptions
try {
// Creating an empty TreeMap
NavigableMap<Integer, String> treemap
= new TreeMap<Integer, String>(
Collections.reverseOrder());
// Populating TreeMap
// using put() method
treemap.put(1, "one");
treemap.put(2, "two");
treemap.put(3, "three");
treemap.put(4, "four");
treemap.put(5, "five");
// Printing the TreeMap
System.out.println("TreeMap: " + treemap);
// Getting used Comparator in the map
// using comparator() method
Comparator comp = treemap.comparator();
// Printing the comparator value
System.out.println("Comparator value: " + comp);
}
// Catch block to handle the exceptions
catch (NullPointerException e) {
// Display message if exception occurs
System.out.println("Exception thrown : " + e);
}
}
}
Output:
TreeMap: {5=five, 4=four, 3=three, 2=two, 1=one}
Comparator value: java.util.Collections$ReverseComparator@232204a1
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