CODEWITHSUNDEEP
java
Abdul Samad
Abdul Samad

Reputation: 29

Avoid NullPointerException from user input

I am using JDK 1.7, I am checking the code for all conditions of input. if user does not enter any value in the String then it throws a NullPointerException. Is there a way to prevent causing NullPointerException even if the user does not enter any value?

i tried try catch block to catch exception

import java.util.*;
import java.io.BufferedReader;
import java.io.InputStreamReader;
class TestClass {
   public static void main(String args[]) throws Exception {

    Scanner s = new Scanner(System.in);    
    int i=s.nextInt();
    System.out.println(i);

    BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
    String str = br.readLine();
    try{
        int length=str.length();  //NullPointerException here

        if(length>=1 && length<=15)
        {
            System.out.println(str);
        }
    }
    catch(NullPointerException e)
    {
        System.out.println("Must enter a string");
    }
   }
}

sample input- 5 null

Expected Output- 5 (Empty string value-> "" but no exception thrown message)

Upvotes: 2

Views: 510

Answers (4)

Oleg Cherednik
Oleg Cherednik

Reputation: 18245

Java 8

int length = Optional.ofNullable(str).orElse("").length();

Java 7

int length = str == null ? 0 : str.length();

Java 7 + Apache Commons

int length = StringUtils.length(str);

Use Scanner

Use Scanner instead of BufferedReader; scane.nextLine() returns not null string.

public static void main(String... args) {
    try (Scanner s = new Scanner(System.in)) {
        System.out.println(s.nextInt());

        s.nextLine();

        String str = s.nextLine();

        if (str.length() >= 1 && str.length() <= 15)
            System.out.println(str);
    }
}

Upvotes: 3

user10762593
user10762593

Reputation:

1) Read the documentation - note that BufferedReader.readline can legitimately return null under well-defined circumstances.

2) Write code that can handle the possible null return.

Upvotes: 0

GothamGirl
GothamGirl

Reputation: 299

import java.util.*;
import java.io.BufferedReader;
import java.io.InputStreamReader;
class TestClass {
   public static void main(String args[]) throws Exception {

    Scanner s = new Scanner(System.in);    
    int i=s.nextInt();
    System.out.println(i);

    BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
    String str = br.readLine();
        if(str!=null && str.length() >=1 && str.length()<=15)
        {
            System.out.println(str);
        }
    }
   }
}

Upvotes: 0

Reto
Reto

Reputation: 1343

Instead of try/catch you could check if str is not null before you call str.length() 

Scanner s = new Scanner(System.in);
String str = s.nextLine();
if (str != null && str.length() <= 15) {
   System.out.println(str);
} else {
   System.out.println("Must enter a string");
}

Upvotes: 0

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