How to fix Cannot invoke "java.util.Map.equals(Object)" because the return value of "java.util.Map.get(Object)" is null

Question

I had to creat a visit card program in java.

package week21;

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

public class _03_ {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        Scanner scanner1 = new Scanner(System.in);
        int o1 = 0, i = 1;
        Map <String,Map<String,String>> Final = new HashMap<>();
        data1 info = new data1();
        while (o1 != 3) {
            System.out.println("What would you like to do:");
            System.out.println("1. Add");
            System.out.println("2. Search");
            System.out.println("3. Exit");
            o1 = scanner1.nextInt();
            if(o1 == 1){
                Map<String,String> save = new HashMap<>();
                System.out.println("Name of owner:");
                String Name = scanner.nextLine();
                save.put("Name", Name);
                System.out.println("Email:");
                String Mail = scanner.nextLine();
                save.put("Mail", Mail);
                System.out.println("Phone number:");
                String Nr = scanner.nextLine();
                save.put("Number", Nr);
                System.out.println("Address:");
                String Address = scanner.nextLine();
                save.put("Address", Address);
                System.out.println("Name of company:");
                String CName = scanner.nextLine();
                Final.put(CName, save);
            }
            else
            if (o1 == 2) {
                System.out.println("What would you like to do:");
                System.out.println("1. A piece of information");
                System.out.println("2. Everything about a company");
                System.out.println("3. Everything");
                int o = scanner.nextInt();
                if (o == 1) {
                    Search(Final);
                } else if (o == 2) {
                    Search2(Final);
                } else if (o == 3) {
                    Search3(Final);
                }
            }
        }
    }
    public static void Search (Map<String, Map<String, String>> Final){
        Scanner scanner = new Scanner(System.in);
        System.out.println("Name of the company");
        String a = scanner.nextLine();
        System.out.println("What information would you like:");
        String b = scanner.nextLine();
        System.out.println(Final.get(a).get(b));
    }
    public static void Search2 (Map<String, Map<String, String>> Final){
        Scanner scanner = new Scanner(System.in);
        System.out.println("What do you know:");
        String s = scanner.nextLine();
        int c = 0;
        for (int i = 0; i < Final.size(); i++) {
            if(Final.get("Name").equals(s)){
                System.out.println(Final.get(i));
                c++;
            } else if (Final.get("Mail").equals(s)) {
                System.out.println(Final.get(i));
                c++;
            } else if (Final.get("Address").equals(s)) {
                System.out.println(Final.get(i));
                c++;
            } else if (Final.get("Phone number").equals(s)) {
                System.out.println(Final.get(i));
                c++;
            }
        }
        if(c == 0){
            System.out.println("It doesn't exist");
        }
    }
    public static void Search3 (Map<String, Map<String, String>> Final){
        System.out.println(Final);
    }
}
class data1{
    String Name;
    String Mail;
    String Nr;
    String Address;
    String CName;
}

When I try to run it it gives me this error:

Exception in thread "main" java.lang.NullPointerException: Cannot invoke "java.util.Map.equals(Object)" because the return value of "java.util.Map.get(Object)" is null at week21.03.Search2(03.java:69) at week21.03.main(03.java:48)

How can I fix it?

Your `Final` doesn't contain the keys `Name`, `Mail` etc. Its keys are names of companies. — RealSkeptic, Jun 20 '22 at 09:50

score 2 · Accepted Answer · answered Jun 20 '22 at 09:53

You defined your map as Map <String,Map<String,String>> Final (please rename your variables, they should start with a lower letter).

As I read your add function correctly the inner map holds some information about a person and this map is stored under the company name. So to get the information you have to read the company name first. If you don't add a person with company name 'Name', 'Mail' and so on Final.get("Name") returns null and you get the NullPointerException. You can iterate over all persons with Final.entrySet().

for (Entry<String, Map<String, String>> entry : m.entrySet()) {
    Map<String, String> person = entry.getValue();
    // your if statements here
}

Additionally your if blocks will always print null because the keys of the map are String and you call get with an int.

How to fix Cannot invoke "java.util.Map.equals(Object)" because the return value of "java.util.Map.get(Object)" is null

1 Answers1