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    java.util.TreeMap.containsKey()方法用于检查特定键是否在TreeMap中映射。它将key元素作为参数,如果该元素在map中映射,则返回True。

    句法:

    Tree_Map.containsKey(key_element)

    参数:该方法只接受一个参数key_element,该参数引用应在地图内检查其映射的键。

    返回值:如果检测到密钥的存在,则该方法返回布尔值true,否则返回false。

    下面的程序用于说明java.util.TreeMap.containsKey()的工作方法

    程序1:将字符串值映射到整数键。

    // Java code to illustrate the containsKey() method
    import java.util.*;
      
    public class Tree_Map_Demo {
        public static void main(String[] args)
        {
      
            // Creating an empty TreeMap
            TreeMap<Integer, String> tree_map = 
            new TreeMap<Integer, String>();
      
            // Mapping string values to int keys
            tree_map.put(10, "Geeks");
            tree_map.put(15, "4");
            tree_map.put(20, "Geeks");
            tree_map.put(25, "Welcomes");
            tree_map.put(30, "You");
      
            // Displaying the TreeMap
            System.out.println("Initial Mappings are: " + tree_map); 
      
            // Checking for the key_element '20'
            System.out.println("Is the key '20' present? " + 
            tree_map.containsKey(20));
      
            // Checking for the key_element '5'
            System.out.println("Is the key '5' present? " + 
            tree_map.containsKey(5));
        }
    }
    

    输出:

    Initial Mappings are: {10=Geeks, 15=4, 20=Geeks, 25=Welcomes, 30=You}
    Is the key '20' present? true
    Is the key '5' present? false

    程序2:将整数值映射到字符串键。

    // Java code to illustrate the containsKey() method
    import java.util.*;
     
    public class Tree_Map_Demo {
        public static void main(String[] args)
        {
     
            // Creating an empty TreeMap
            TreeMap<String, Integer> tree_map = 
            new TreeMap<String, Integer>();
     
            // Mapping int values to string keys
            tree_map.put("Geeks", 10);
            tree_map.put("4", 15);
            tree_map.put("Geeks", 20);
            tree_map.put("Welcomes", 25);
            tree_map.put("You", 30);
     
            // Displaying the TreeMap
            System.out.println("Initial Mappings are: " + tree_map); 
     
            // Checking for the key_element 'Welcomes'
            System.out.println("Is the key 'Welcomes' present? " +  
            tree_map.containsKey("Welcomes"));
     
            // Checking for the key_element 'World'
            System.out.println("Is the key 'World' present? " + 
            tree_map.containsKey("World"));
        }
    }
    

    输出:

    Initial Mappings are: {4=15, Geeks=20, Welcomes=25, You=30}
    Is the key 'Welcomes' present? true
    Is the key 'World' present? false

    注意:对于具有不同数据类型的变体和组合的任何类型的映射,都可以执行相同的操作。

     
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