User Management in Java- This program enters users details (name, address, city, date of birth, phone number, email Id). It then maps phone numbers to names with the help of HashMap. Finally, it tells the name of the user which is searched by entering the phone number.

Application.java

package com.company;

import java.util.HashMap;
import java.util.Map;
import java.util.HashMap;

public class Application {
    static Map<String, User> userStorage = new HashMap<>();
    public static void main(String[] args) {
        System.out.println("****************Diamond Store************");
        UserService userService = new UserService();
        User user = userService.getUserDetails();
        userStorage.put(user.getPhone_no(), user);

        String mobileNumberToSearch = userService.findUserDetails();
        User userFromStore = userStorage.get(mobileNumberToSearch);

        userService.printUserDetails(userFromStore);
    }
}

User.java

package com.company;
import java.io.*;
import java.util.*;
import java.text.*;
import java.lang.*;
import java.util.HashMap;
import java.util.Map;

    public class User {
        private String name;
        private String address;
        private String city;
        private String dob;
        private String phone_no;
        private String emailId;

        public String getName() {
            return name;
        }

        public void setName(String name) {
            this.name = name;
        }

        public String getAddress() {
            return address;
        }

        public void setAddress(String address) {
            this.address = address;
        }

        public String getCity() {
            return city;
        }

        public void setCity(String city) {
            this.city = city;
        }

        public String getDob() {
            return dob;
        }

        public void setDob(String dob) {
            this.dob = dob;
        }

        public String getPhone_no() {
            return phone_no;
        }

        public void setPhone_no(String phone_no) {
            this.phone_no = phone_no;
        }

        public String getEmailId() {
            return emailId;
        }

        public void setEmailId(String emailId) {
            this.emailId = emailId;
        }
    }

UserService.java

package com.company;
import java.util.HashMap;
import java.util.Map;
import java.util.Scanner;

public class UserService {
    public User getUserDetails() {
        User user = new User();
        Scanner scanner = new Scanner(System.in);
        System.out.println("==============User Details Input=================");
        System.out.println("Please enter you name : ");
        String name = scanner.nextLine();
        if (name == null || name.isEmpty()) {
            System.out.println("Please enter a valid name");
        }
        user.setName(name);
        System.out.println("enter your address ");
        String address = scanner.nextLine();
        user.setAddress(address);
        System.out.println("enter your city ");
        String city = scanner.nextLine();
        user.setCity(city);
        System.out.println("enter your date of birth ");
        String dob = scanner.nextLine();
        user.setDob(dob);
        System.out.println("enter phone number");
        String phone_no = scanner.nextLine();
        user.setPhone_no(phone_no);
        System.out.println("enter email");
        String emailID = scanner.nextLine();
        user.setEmailId(emailID);

        return user;
    }
    public String findUserDetails() {
        System.out.println("Mobile Number to search : ");
        Scanner scanner = new Scanner(System.in);
        String phone = scanner.nextLine();
        return phone;
    }

    public void printUserDetails(User userFromStore) {
        System.out.println("user searched is : "+userFromStore.getName());
    }
}