Java中的Java .util.TreeMap.floorEntry() 和 floorKey()

在许多地方都使用找到小于给定值的最大数字，并且在基于地图的容器中具有该功能始终是一个优点。 Java.util.TreeMap 还使用 floor()函数提供此功能。有 2 种变体，下面将讨论这两种变体。 1. floorEntry() ：它返回与小于或等于给定键的最大键关联的键值映射，如果没有这样的键，则返回 null。

Parameters:
key : This is the key to be matched.
Return Value:
It returns an entry with the greatest key less than or equal to key,
or null if there is no such key.
Exception:
ClassCastException : This exception is thrown if the specified
key cannot be compared with the keys currently in the map.
NullPointerException : This exception is thrown if the specified
key is null and this map uses natural ordering, or its comparator does not permit null keys.

// Java code to demonstrate the working
// of floorEntry()
import java.io.*;
import java.util.*;
public class floorEntry {
    public static void main(String[] args)
    {
  
        // Declaring the tree map of Integer and String
        TreeMap tmp = new TreeMap();
  
        // assigning the values in the tree map
        // using put()
        tmp.put(10, "ten");
        tmp.put(7, "seven");
        tmp.put(19, "nineteen");
        tmp.put(3, "three");
  
        // use of floorEntry()
        // displays the floor value of 6
        // prints 3=three
        System.out.println("The greatest key-value less than 6 is : " 
        + tmp.floorEntry(6));
    }
}

输出：

The greatest key-value less than 6 is : 3=three

2. floorKey() ：返回小于或等于给定键的最大键，如果没有这样的键，则返回null。

Parameters:
key : This is the key to be matched.
Return Value:
It returns an entry with the greatest key less than or equal to key, or
null if there is no such key.
Exception:
ClassCastException : This exception is thrown if the specified
key cannot be compared with the keys currently in the map.
NullPointerException : This exception is thrown if the specified key
is null and this map uses natural ordering, or its comparator does not permit null keys.

// Java code to demonstrate the working
// of floorKey()
import java.io.*;
import java.util.*;
public class floorKey {
    public static void main(String[] args)
    {
  
        // Declaring the tree map of Integer and String
        TreeMap tmp = new TreeMap();
  
        // assigning the values in the tree map
        // using put()
        tmp.put(10, "ten");
        tmp.put(7, "seven");
        tmp.put(19, "nineteen");
        tmp.put(3, "three");
  
        // use of floorKey()
        // displays the floor key of
        // prints 3
        System.out.println("The greatest key less than 6 is : "
        + tmp.floorKey(6));
    }
}

输出：

The greatest key less than 6 is : 3

实际应用：此功能的可能应用很多。从给定汽油的最大距离或给定成分的可能菜肴开始。前一个在下面的代码中讨论。

// Java code to demonstrate the application
// of floorKey() and floorEntry
import java.io.*;
import java.util.*;
public class floorappli {
    public static void main(String[] args)
    {
  
        // Declaring the tree map of Integer and String
        TreeMap destin = new TreeMap();
  
        // assigning the km with destination
        // from beginning
        // using put()
        destin.put(10, "Delhi");
        destin.put(7, "Gurgaon");
        destin.put(19, "Noida");
        destin.put(3, "Ring Road");
  
        // Entering the available Petrol (consider 1km/litre)
        int petr = 12;
  
        // Maximum place you can reach
        System.out.println("The maximum place you can reach with given petrol : "
        + destin.floorEntry(petr));
    }
}

输出：

The maximum place you can reach with given petrol : 10=Delhi