Java TreeMap.descendingMap()、descendingKeyset()用法及代码示例

Java.util.TreeMap中有descending()的两个变体，本文都将进行讨论。 1. descendingKeySet()：它返回Map中包含的键的逆序可导航Set视图。

用法：
public NavigableSet descendingKeySet()
参数：
NA
返回值：
It returns a reverse order navigable set view of the keys in this map.
Exception:
NA

// Java code to demonstrate the working 
// descendingKeySet() 
import java.io.*; 
import java.util.*; 
public class descendingKeySet1 { 
public static void main(String[] args) 
    { 
  
        // Declaring the tree map of Integer and String 
        TreeMap<Integer, String> treemap = new TreeMap<Integer, String>(); 
  
        // assigning the values in the tree map 
        // using put() 
        treemap.put(2, "two"); 
        treemap.put(0, "zero"); 
        treemap.put(3, "three"); 
        treemap.put(6, "six"); 
        treemap.put(9, "nine"); 
        treemap.put(7, "seven"); 
  
        // putting values in navigable set 
        // use of descendingKeySet 
        NavigableSet set1 = treemap.descendingKeySet(); 
  
        System.out.println("Navigable set values are:" + set1); 
    } 
}

输出：

Navigable set values are:[9, 7, 6, 3, 2, 0]

2. descendingMap()：它返回映射中包含的映射的逆序视图。

用法：
public NavigableMap descendingMap()
参数：
NA
Return Value
It returns a reverse order view of the map.
Exception:
NA

// Java code to demonstrate the working 
// of descendingMap() 
import java.io.*; 
import java.util.*; 
public class descendingMap { 
public static void main(String[] args) 
    { 
  
        // Declaring the tree map of Integer and String 
        TreeMap<Integer, String> treemap = new TreeMap<Integer, String>(); 
  
        // assigning the values in the tree map 
        // using put() 
        treemap.put(2, "two"); 
        treemap.put(0, "zero"); 
        treemap.put(3, "three"); 
        treemap.put(6, "six"); 
        treemap.put(9, "nine"); 
        treemap.put(7, "seven"); 
  
        // putting values in navigable map 
        // use of descendingMap() 
        NavigableMap map1 = treemap.descendingMap(); 
  
        System.out.println("Navigable map values are:" + map1); 
    } 
}

输出：

Navigable map values are:{9=nine, 7=seven, 6=six, 3=three, 2=two, 0=zero}

实际应用：本文介绍了降序函数的许多应用。其中一些是优先级调度或设计排名系统。下面的代码演示了后者。

// Java code to demonstrate the application 
// of descendingMap() and descendingKetSet() 
import java.io.*; 
import java.util.*; 
public class descendingAppli { 
public static void main(String[] args) 
    { 
  
        // Declaring the tree map of Integer and String 
        // to store participants info of scores with name 
        TreeMap<Integer, String> participants = new TreeMap<Integer, String>(); 
  
        // assigning score of participants 
        // using put() 
        participants.put(30, "Ashty"); 
        participants.put(45, "Shavi"); 
        participants.put(16, "Vaish"); 
        participants.put(15, "Kil"); 
        participants.put(11, "Manju"); 
  
        // putting ranks in NavigableMap 
        // use of descendingMap() to assign 1st to 
        // maximum values and so on 
        NavigableMap<Integer, String> Ranks = participants.descendingMap(); 
  
        System.out.println("The ranks according to scores are:"); 
  
        // Printing values rankwise 
        int count = 0; 
        for (NavigableMap.Entry<Integer, String> entry:Ranks.entrySet()) { 
            count++; 
            String str = Integer.toString(count); 
            System.out.println("Rank " + str + ":" + entry.getValue()); 
        } 
    } 
}

输出：

The ranks according to scores are:
Rank 1:Shavi
Rank 2:Ashty
Rank 3:Vaish
Rank 4:Kil
Rank 5:Manju

相关用法

注：本文由纯净天空筛选整理自 Java.util.TreeMap.descendingMap() and descendingKeyset() in Java。非经特殊声明，原始代码版权归原作者所有，本译文未经允许或授权，请勿转载或复制。