java treemap_Java TreeMap firstKey（）方法与示例

落日映苍穹つ 2023-03-05 15:53 9阅读 0赞

java treemap

## TreeMap类firstKey()方法 **(**TreeMap Class firstKey() method**)** ##

*  **firstKey() method** is available in java.util package.
    
    **firstKey()方法**在java.util包中可用。
 *  **firstKey() method** is used to return the first key element with the least key value that exists in this TreeMap.
    
    **firstKey()方法**用于返回此TreeMap中具有最小键值的第一个键元素。
 *  **firstKey() method** is a non-static method, it is accessible with the class object only and if we try to access the method with the class name then we will get an error.
    
    **firstKey()方法**是一种非静态方法，只能通过类对象访问，如果尝试使用类名称访问该方法，则会收到错误消息。
 *  **firstKey() method** may throw an exception at the time of returning the first key element with the lowest key value.
    
    **firstKey()方法**在返回具有最低键值的第一个键元素时可能会引发异常。
    
    **NoSuchElementException**: This exception may throw when this TreeMap is “blank”.
    
    **NoSuchElementException** ：当此TreeMap为“空白”时，可能引发此异常。

**Syntax:**

**句法：**

public Key firstKey();

**Parameter(s):**

**参数：**

*  It does not accept any parameter.
    
    它不接受任何参数。

**Return value:**

**返回值：**

The return type of the method is Key, it retrieves first key element with the lowest key value.

该方法的返回类型为Key ，它检索具有最低键值的第一个键元素。

**Example:**

**例：**

// Java program to demonstrate the example 
    // of Key firstKey() method of TreeMap 
    
    import java.util.*;
    
    public class FirstKeyOfTreeMap {
        
        public static void main(String[] args) {
        
            // Instantiates a TreeMap object
            TreeMap < Integer, String > tree_map = new TreeMap < Integer, String > ();
    
            // By using put() method is to add
            // key-value pairs in a TreeMap
            tree_map.put(20, "C");
            tree_map.put(50, "C++");
            tree_map.put(30, "JAVA");
            tree_map.put(10, "PHP");
            tree_map.put(60, "SFDC");
    
            // Display TreeMap 
            System.out.println("TreeMap: " + tree_map);
    
            // By using firstKey() method is to return
            // the first least key value
            // element exists in this TreeMap
            System.out.println("tree_map.firstKey(): " + tree_map.firstKey());
        }
    }

**Output**

**输出量**

TreeMap: {10=PHP, 20=C, 30=JAVA, 50=C++, 60=SFDC}
    tree_map.firstKey(): 10

> 翻译自: [https://www.includehelp.com/java/treemap-firstkey-method-with-example.aspx][https_www.includehelp.com_java_treemap-firstkey-method-with-example.aspx]

java treemap

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