HashMap in Java

HashMap

HashMap stores data in key-value pairs. If you want to store values like {address=USA, fathername=Himal Sharma}. You can store data in a hash map. You must import java.util.HashMap;

Syntax

import java.util.HashMap; // First Import this

HashMap<String, String> personalDetails = new HashMap<String, String>();

For String Key And Double Value

HashMap<String, Double> hashMapName = new HashMap<String, Double>();

For Int Key And String Value

HashMap<Integer, String> hashMapName = new HashMap<Integer, String>();

Example


import java.util.HashMap;

public class Main {
    public static void main(String[] args) {
        // Create a HashMap object i.e personalDetails
        HashMap<String, String> personalDetails = new HashMap<String, String>();

       // Adding Keys and Values.
        personalDetails.put("name", "Milan Sharma");
        personalDetails.put("address", "USA");
        personalDetails.put("fathername", "Himal Sharma");
        personalDetails.put("mothername", "Sita Sharma");
        System.out.println(personalDetails);
    }
}
Show Output

Some Useful Methods For HashMap

Here personalDetails is HashMap variable. You can create a variable with any name. You can create of any type.

Methods Description
personalDetails.get(“name”); To Access item. prints Milan Sharma
personalDetails.remove(“name”); Removes item. remove Milan Sharma and USA
personalDetails.clear(); Clear all items
personalDetails.size(); Get size of HashMap

Loop Through HashMap / Print All Keys

// Print all keys
for (String i : personalDetails.keySet()) {
  System.out.println(i);
}

To Print All Values

// Print all values
for (String i : personalDetails.values()) {
  System.out.println(i);
}

To Print Keys And Values

// Print keys and values
for (String i : personalDetails.keySet()) {
  System.out.println("key is: " + i + " value is: " + personalDetails.get(i));
}

Example: Java Program To Store Name and Salary

import java.util.HashMap;

public class Main {
    public static void main(String[] args) {
        // Create a HashMap object i.e salaries
        HashMap<String, Double> salaries = new HashMap<String, Double>();

       // Adding name and salary.
        salaries.put("Ram Sharma", 1100.0);
        salaries.put("Hari Sharma",1200.0 );
        salaries.put("Rocky Yadav", 2550.0);
        salaries.put("Menuka Pradhan", 1500.0);

        for (String name : salaries.keySet()) {
            System.out.println( name + " salary is : " + salaries.get(name));
        }
    }
}
Show Output