Java Map中value()与 entrySet()方法的区别

地图接口存在于Java.util包中，它主要提供了三个方法KeySet()、entrySet()和values()。这些方法分别用于检索地图的键、地图的键值对以及地图的值。由于这些方法是地图接口的一部分，所以我们可以在所有实现地图接口的类中使用这些方法，比如TreeMap、HashMap和LinkedHashMap。

方法1： 价值()_方法

Java中HashMap类的java.util.HashMap.values()方法用于从地图的值中创建一个集合。它基本上返回HashMap中数值的一个集合视图。

语法:

Hash_Map.values()

参数： 该方法不接受任何参数。

返回值： 该方法用于返回一个包含地图所有值的集合视图。

示例:

// Java program demonstrating use of values() method
 
// Importing all input output classes
import java.io.*;
// Importing HashMap, Iterator, Map and Stream classes
// from the java.util package
import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;
import java.util.stream.Stream;
 
// Class
class GFG {
 
    // Main driver method
    public static void main(String[] args)
    {
        // Creating a Map object
        // Declaring object of String and integer type
        Map<Integer, String> map = new HashMap<>();
 
        // Now, adding the elements to the object created
        // Elements here are key- \value pairs
 
        // Custom input objects
        map.put(1, "Geeks");
        map.put(2, "For");
        map.put(3, "Geeks");
 
        // Showcasing different ways to illustrate
        // values() method
 
        // Way 1 - Using iterator
        // Iterating over the object elements of the
        // showcasing the values() method using iterator
 
        // Creating an object of Integer type
        Iterator<String> itr = map.values().iterator();
 
        // Condition check which holds true till
        // there is single elementusing hasNext() method
        while (itr.hasNext()) {
 
            // Traversing across the elements
            // using next() method
 
            // Printing the elements in the object
            System.out.print(itr.next() + " ");
        }
 
        // New line
        System.out.println();
 
        // Way 2 - Using loops
        // Iterating over the elements using for-each loop
        // to showacase value() method
        for (String key : map.values()) {
 
            // Printing all the element in object
            // key-value pairs
            System.out.println(key);
        }
 
        // New line
        System.out.println();
 
        // Iterating over the values() method by
        // converting the Map to the string
        System.out.println(map.values().toString());
    }
}

输出

Geeks For Geeks 
Geeks
For
Geeks

[Geeks, For, Geeks]

方法2： entrySet()方法

Java中的java.util.HashMap.entrySet()方法是用来从哈希图中包含的相同元素中创建一个集合。它基本上返回散列图的集合视图，或者我们可以创建一个新的集合，并将地图元素存储到其中。

语法:

hash_map.entrySet()

参数： 该方法不接受任何参数。

返回值： 该方法返回一个具有与哈希图相同元素的集合。

实现。

示例

// Java program demonstrating use of entrySet() method
 
//  Importing Map,Stream, hashMap and Iterator classes
// from the java.util package
import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;
import java.util.stream.Stream;
 
// Class
class GFG {
 
    // Main driver method
    public static void main(String[] args)
    {
        // Creating an object of Map class
        // Declaring object of Integer and String type
        Map<Integer, String> map = new HashMap<>();
 
        // Now, adding the elements to the object
        // Here elements are key-value pairs to map
 
        // Custom input elements
        map.put(1, "Geeks");
        map.put(2, "For");
        map.put(3, "Geeks");
 
        // Now, proposing different cases in which we will
        // be iterating over the elements using entrySet()
 
        // Case 1
        // Iterating the key value pairs
        // using for each loop
        for (Map.Entry<Integer, String> entry :
             map.entrySet()) {
 
            // Corresponding key
            Integer key = (Integer)entry.getKey();
 
            // Corresponding pair
            String value = entry.getValue();
 
            // Printing all the corresponding key-value
            // pairs
            System.out.println(key + "=" + value);
        }
 
        // Case 2
        // Iterating the key-value pairs
        // using iterator
        Iterator<Map.Entry<Integer, String> > itr
            = map.entrySet().iterator();
 
        // Condition check using hasNext() method holding
        // true till there is single entry remaining
        while (itr.hasNext()) {
 
            // Go on printing key-value pairs
            System.out.println(itr.next());
        }
 
        // Case 3
        // Iterating and printing the key-value pairs
        // using Stream.of() method
 
        // Printing alongside by using scope resolution
        // operator
        Stream.of(map.entrySet().toArray())
            .forEach(System.out::println);
    }
}

输出

1=Geeks
2=For
3=Geeks
1=Geeks
2=For
3=Geeks
1=Geeks
2=For
3=Geeks

现在让我们来看看values()方法和entrySet()方法的区别