Java TreeMap firstEntry()用法及代码示例

TreeMap firstEntry()是指用于检索与TreeMap中存在的最低键值元素映射的键值对的方法，如果Map中没有键值对，则仅返回null。方法名称“ firstEntry()”本身说明，它将返回键元素最少的条目及其值。

Syntax:public Map.Entry<K,V> firstEntry(), 

Here K and V refer key-value respectively.

Parameters:NA - As it doesnot accept any parameter.

Return Value: It returns an entry with the least key (lowest key-value pair) and null if the 
TreeMap is empty.

Exception:NA - As it doesnot throw any exception at entry return.

范例1：

Java

// Java code to demonstrate  
// the working of TreeMap firstKey()  
import java.io.*;  
import java.util.*;  
public class treeMapFirstKey {  
public static void main(String[] args)  
    {  
    
        // Declaring the TreeMap of Key - Value Pairs 
        // Integer - Key , String - Value 
        TreeMap<Integer, String> treemap = new TreeMap<Integer, String>();  
    
        // Adding-up the values in the TreeMap  
        // Use put() function to append data  
        treemap.put(2, "Java");  
        treemap.put(4, "CPP");  
        treemap.put(5, "PHP");  
        treemap.put(1, "Python");  
        treemap.put(3, "C");  
    
        // Check for firstEntry() 
        System.out.println("Lowest Entry is:" + treemap.firstEntry());  
    }  
}

输出

Lowest Entry is:1=Python

在上面的示例中，很明显firstEntry()检查会比较TreeMap的每个键，并返回键值对最小的键。

范例2：

Java

// Java code to demonstrate the working 
// of TreeMap firstKey() method 
import java.io.*;  
import java.util.*;  
public class percentageFirstKey {  
public static void main(String[] args)  
    {  
    
        // Declaring the TreeMap of Key - Value Pairs 
        // Double - Key , String - Value 
        TreeMap<Double, String> treemapPercentage = new TreeMap<Double, String>();  
    
        // Adding-up the values in the TreeMap  
        // Use put() function to append data  
        treemapPercentage.put(81.40, "Shashank");  
        treemapPercentage.put(72.80, "Anand"); 
        treemapPercentage.put(65.50, "Gulshan"); 
        treemapPercentage.put(71.10, "Abhishek");  
        treemapPercentage.put(70.20, "Ram");  
    
        // Check for firstEntry() 
        System.out.println("Lowest Entry is:" + treemapPercentage.firstEntry());  
    }  
}

输出

Lowest Entry is:65.5=Gulshan

TreeMap firstEntry()上的一些要点：

TreeMap firstEntry()在java.util软件包中可用。
在返回条目时它不会引发异常。
TreeMap firstEntry()方法是非静态方法，因为类的对象可以访问该方法，否则将产生错误。

相关用法

注：本文由纯净天空筛选整理自night_fury1大神的英文原创作品 TreeMap firstEntry() Method in Java with Examples。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。