Java中的 TreeMap keySet() 方法及示例
在Java中,TreeMap 类的keySet() 方法存在于Java中的Java .util 包中,用于从树形图中包含的关键元素创建一个集合。它基本上返回键的集合视图,或者我们可以创建一个新集合并按升序将键元素存储在其中。由于该集合由地图支持,因此对地图所做的任何更改都会反映在该集合中,反之亦然。
--> java.util Package
--> TreeMap Class
--> keySet() Method
句法:
tree_map.keySet()
返回类型:树形图的键按升序排列的集合。
示例 1:将字符串值映射到整数键。
Java
// Java Program to illustrate the keySet() method
// of TreeMap class where we are
// Mapping String Values to Integer Keys
// Importing required classes
import java.util.*;
// Main class
public class GFG {
// MAin driver method
public static void main(String[] args)
{
// Creating an empty TreeMap by
// declaring object of integer, string pairs
TreeMap tree_map
= new TreeMap();
// Mapping string values to int keys
// using put() method
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");
// Printing the elements of above TreeMap
System.out.println("Initial Mappings are: "
+ tree_map);
// Getting the set view of keys
// using keySet() method
System.out.println("The set is: "
+ tree_map.keySet());
}
}
Java
// Java Program to Illustrate keySet() Method
// of TreeMap class where we are
// Mapping Integer Values to String Keys
// Importing required classes
import java.util.*;
// Main class
public class GFG {
// Main driver method
public static void main(String[] args)
{
// Creating an empty TreeMap by
// declaring object of string, integer pairs
TreeMap tree_map
= new TreeMap();
// Mapping int values to string keys
// using put() method
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);
// Printing the elements of TreeMap
System.out.println("Initial Mappings are: "
+ tree_map);
// Getting the set view of keys
// using keySet() method
System.out.println("The set is: "
+ tree_map.keySet());
}
}
输出:
Initial Mappings are: {10=Geeks, 15=4, 20=Geeks, 25=Welcomes, 30=You}
The set is: [10, 15, 20, 25, 30]
示例 2:将整数值映射到字符串键
Java
// Java Program to Illustrate keySet() Method
// of TreeMap class where we are
// Mapping Integer Values to String Keys
// Importing required classes
import java.util.*;
// Main class
public class GFG {
// Main driver method
public static void main(String[] args)
{
// Creating an empty TreeMap by
// declaring object of string, integer pairs
TreeMap tree_map
= new TreeMap();
// Mapping int values to string keys
// using put() method
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);
// Printing the elements of TreeMap
System.out.println("Initial Mappings are: "
+ tree_map);
// Getting the set view of keys
// using keySet() method
System.out.println("The set is: "
+ tree_map.keySet());
}
}
输出:
Initial Mappings are: {4=15, Geeks=20, Welcomes=25, You=30}
The set is: [4, Geeks, Welcomes, You]
Note: Similarly the same operation can be performed with any type of Mappings with variation and combination of different data types.