Java TreeMap navigableKeySet()方法及示例

java.util.TreeMap 类的 navigableKeySet() 方法用于返回该地图中包含的键的NavigableSet视图。
该集合的迭代器按升序返回键。这个集合是由地图支持的，所以地图的变化会反映在集合中，反之亦然。如果在集合的迭代过程中修改了地图（除了通过迭代器自身的移除操作），那么迭代的结果将无法定义。集支持元素移除，通过Iterator.remove、Set.remove、removeAll、retainAll和clear操作从地图中移除相应的映射。它不支持add或addAll操作。
语法：

public NavigableSet navigableKeySet()

返回值： 该方法返回该地图中键值的 可导航集合视图 。

下面是说明navigableKeySet()方法的例子

例子1：

// Java program to demonstrate
// navigableKeySet() method
// for Integer value key
 
import java.util.*;
 
public class GFG1 {
    public static void main(String[] argv)
        throws Exception
    {
 
        try {
 
            // creating object of TreeMap<Integer, String>
            TreeMap<Integer, String>
                treemap = new TreeMap<Integer, String>();
 
            // populating tree map
            treemap.put(1, "One");
            treemap.put(2, "Two");
            treemap.put(3, "Three");
            treemap.put(4, "Four");
            treemap.put(5, "Five");
 
            // printing the TreeMap
            System.out.println("TreeMap: " + treemap);
 
            // getting navigable set view of the keys
            // using navigableKeySet() method
            NavigableSet<Integer>
                value = treemap.navigableKeySet();
 
            // printing the value
            System.out.println("Value is: " + value);
        }
 
        catch (NullPointerException e) {
            System.out.println("Exception thrown : " + e);
        }
    }
}

输出

TreeMap: {1=One, 2=Two, 3=Three, 4=Four, 5=Five}
Value is: [1, 2, 3, 4, 5]

例2：

// Java program to demonstrate
// navigableKeySet() method
// for String value key
 
import java.util.*;
 
public class GFG1 {
    public static void main(String[] argv)
        throws Exception
    {
 
        try {
 
            // creating object of TreeMap<Integer, String>
            TreeMap<String, Integer>
                treemap = new TreeMap<String, Integer>();
 
            // populating tree map
            treemap.put("A", 1);
            treemap.put("B", 2);
            treemap.put("C", 3);
            treemap.put("D", 4);
            treemap.put("E", 5);
 
            // printing the TreeMap
            System.out.println("TreeMap: " + treemap);
 
            // getting navigable set view of the keys
            // using navigableKeySet() method
            NavigableSet<String>
                value = treemap.navigableKeySet();
 
            // printing the value
            System.out.println("Value is: " + value);
        }
 
        catch (NullPointerException e) {
            System.out.println("Exception thrown : " + e);
        }
    }
}

输出

TreeMap: {A=1, B=2, C=3, D=4, E=5}
Value is: [A, B, C, D, E]