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In this example, we will learn to iterate over the keys, values, and entries of Java HashMap/value mapping.
To understand this example, you should be familiar with the followingJava ProgrammingTopic:
In Java HashMap, we can iterate over itskeys,valuesandkey / valueMapping.
import java.util.HashMap;
import java.util.Map.Entry;
class Main {
public static void main(String[] args) {
//Create a HashMap
HashMap<String, String> languages = new HashMap<>();
languages.put("Java", "Enterprise");
languages.put("Python", "ML/AI");
languages.put("JavaScript", "Frontend");
System.out.println("HashMap: "); + languages);
//Traverse keys/Value mapping
System.out.print("Entries: ");
for(Entry<String, String> entry : languages.entrySet()) {
System.out.print(entry);
System.out.print(", ");
}
//Traverse keys
System.out.print("\nKeys: ");
for(String key : languages.keySet()) {
System.out.print(key);
System.out.print(", ");
}
// Traverse values
System.out.print("\nValues: ");
for(String value : languages.values()) {
System.out.print(value);
System.out.print(", ");
}
}
}Output result
HashMap: {Java=Enterprise, JavaScript=Frontend, Python=ML}/AI}
Entries: Java=Enterprise, JavaScript=Frontend, Python=ML/AI,
Keys: Java, JavaScript, Python,
Values: Enterprise, Frontend, ML/AI,In the above example, we created a hash map named languages. Here, we use the forEach loop to iterate over the elements of the hash map.
Note that we traverse independentlykey,valuesandkey / valueMapping.
language.entrySet() - Returns a set collection view of all entries
language.keySet() -Returns a set collection view of all keys
language.values() -Returns a set collection view of all values
Note：We have used the Map.Entry class. The nested class returns a map view.
import java.util.HashMap;
import java.util.Iterator;
import java.util.Map.Entry;
class Main {
public static void main(String[] args) {
//Create a HashMap
HashMap<String, String> languages = new HashMap<>();
languages.put("Java", "Enterprise");
languages.put("Python", "ML/AI");
languages.put("JavaScript", "Frontend");
System.out.println("HashMap: "); + languages);
//Create an Iterator object
Iterator<Entry<String, String>> iterate1 = languages.entrySet().iterator();
//Traverse keys/Value mapping
System.out.print("Entries: ");
while(iterate1.hasNext()) {
System.out.print(iterate1.next());
System.out.print(", ");
}
//Traverse keys
Iterator<String> iterate2 = languages.keySet().iterator();
System.out.print("\nKeys: ");
while(iterate2.hasNext()) {
System.out.print(iterate2.next());
System.out.print(", ");
}
//Traverse values
Iterator<String> iterate3 = languages.values().iterator();
System.out.print("\nValues: ");
while(iterate3.hasNext()) {
System.out.print(iterate3.next());
System.out.print(", ");
}
}
}Output result
HashMap: {Java=Enterprise, JavaScript=Frontend, Python=ML}/AI}
Entries: Java=Enterprise, JavaScript=Frontend, Python=ML/AI,
Keys: Java, JavaScript, Python,
Values: Enterprise, Frontend, ML/AI,In the above example, we traverse the keys, values, and entries of the hash map./Value mapping. We used the iterator() method to iterate over the hash map. Here,
hasNext() - Returns true if there is a next element in the hashmap.
next() - Return the next element of the hash map.
Note: We can also useHashMap forEach()Method to iterate over a hash map.