CodeGym/Help with Java Tasks/I can't find the problem

Level 20

Warsaw

27.04.2020
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22comments

I can't find the problem

Question about the task

Functionality is not enough!

Java Syntax, Level 10, Lesson 11

Resolved

I get NumberFormatException: For input string: "String1" but I can't find out why, please help me :)

Task: The program reads a pair (a number and string) from the keyboard and displays it on the screen.
New task: The program reads pairs (a number and string) from the keyboard and stores them in a HashMap.
Any empty input signifies the end of data entry.
The numbers can be repeated.
The strings are always unique.
The entered data must not be lost!
The program then displays the contents of the HashMap on the screen.
Each pair on a new line.

Example input:
1 Sam 2 I 1 Am

Example output:
1 Sam 2 I 1 Am

Requirements:

The program must read data from the keyboard.
The program should display text on the screen.
In the main method, declare a HashMap variable and immediately initialize it.
The program should put the pairs read from the keyboard into the HashMap.
The program should display the contents of the HashMap in accordance with the conditions. The key and value are separated by a space. Each value should be on a new line.

package com.codegym.task.task10.task1019; import java.io.*; import java.util.*; /* Functionality is not enough! */ public class Solution { public static void main(String[] args) throws IOException { BufferedReader reader = new BufferedReader(new InputStreamReader(System.in)); Map<String, Integer> map = new HashMap<>(); while(true){ if (reader.readLine().isEmpty()){ break; } else{ Integer id = Integer.parseInt(reader.readLine()); String name = reader.readLine(); if (name.isEmpty()){ map.put(name, id); break; } else{ map.put(name, id); } } } for(Map.Entry<String, Integer> pair : map.entrySet()){ System.out.println("Id=" + pair.getValue() + " Name=" + pair.getKey()); } } }

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Stefan Maric

Level 22 , Frankfurt , Germany

27 April 2020, 18:29

You will have to change your logic, this is a tricky task. Try this: while (true) { read String x if (if x is empty) { break; } int id = Intege.parseInt(x); read string name; if ( if name is empty) { map.put(name, id); break; } map.put(name, id); } also, change your print command to " value + " " + key " validator will give not verify if you don't print by correct explanation.

Agata

Level 20 , Warsaw, Poland

27 April 2020, 19:47

I think I followed your comment correctly but now I get NullPointerException... while(true){ String s = reader.readLine(); if (s.isEmpty()){ break; } Integer id = Integer.parseInt(s); String name = reader.readLine(); if (name.isEmpty()){ map.put(name, id); break; } map.put(name, id); } for(Map.Entry<String, Integer> pair : map.entrySet()){ String key = pair.getKey(); int value = pair.getValue(); System.out.println("Id=" + value + " Name=" + key); }

Agata

Level 20 , Warsaw, Poland

28 April 2020, 07:33

changed again to: System.out.println( value + " " + key); and added try{} catch{}, so now the only requirement that is not met is "declare a HashMap variable and immediately initialize it." and I don't understand why...

Stefan Maric

Level 22 , Frankfurt , Germany

28 April 2020, 16:34

In your if statement try comparing entered string to empty one : while (true) { String value = reader.readLine(); if (value.equals("")) { break; } int id = Integer.parseInt(value); String name = reader.readLine(); if (name.equals("")) { map.put(name, id); break; } map.put(name, id); }

Stefan Maric

Level 22 , Frankfurt , Germany

28 April 2020, 16:36

And also when you are printing your map change System.out.println("Id=" + value + " Name=" + key); to: System.out.println(value + " " + key);

Agata

Level 20 , Warsaw, Poland

29 April 2020, 10:44

It was still NullPointer with ".equals("")" but I changed it to this form and there is no exception anymore: while(true){ String s = reader.readLine(); if ((s==null) || (s.isEmpty())){ break; } Integer id = Integer.parseInt(s); String name = reader.readLine(); if ((name==null) || (name.isEmpty())){ map.put("", id); break; } map.put(name, id); } for(Map.Entry<String, Integer> pair : map.entrySet()){ System.out.println(pair.getValue() + " " + pair.getKey()); } However I do not meet "declare a HashMap variable and immediately initialize it." requirement which is very confusing...

Stefan Maric

Level 22 , Frankfurt , Germany

29 April 2020, 12:35

You are confusing your self. :) Compare this with your code and try to understand: while (true) { // Infinite while loop String value = reader.readLine(); // Reading value as String because you have to break if "String" is empty if (value.equals("")) { // If user enters empty String then break. break; } int id = Integer.parseInt(value); // In this statement you are creating int primitive and turning String from above to int! not Integer object. String name = reader.readLine(); // Now you are reading your String which is your key in hasMap. if (name.equals("")) { // Again you will have to check if is empty and if it is you will add empty String (null) as a key and int which you have read in line above, map.put(name, id); // ,on this way you will not lose any data as task is asking you to do. break; } map.put(name, id); // In this case if non of above reading is not true in you condition you will add String as a key and int as a value. } Compare completely my code with yours and you will see your mistake. You have to add primitives to hashMap, and you are not doing that. Also when comparing empty String use stringName.equals(""); in which you are comparing correctly.

Stefan Maric

Level 22 , Frankfurt , Germany

29 April 2020, 12:57

in your code that you post above mistakes are: while(true){ String s = reader.readLine(); if ((s==null) || (s.isEmpty())){ // in this case you will have to compare s.equals("") break; } Integer id = Integer.parseInt(s); // here you have to use primitive ( int ), and assign it parsed value of s String name = reader.readLine(); if ((name==null) || (name.isEmpty())){ // should be same as above reading map.put("", id); // here you are assigning empty String instead of "name" variable that you declared previously. break; } map.put(name, id); } for(Map.Entry<String, Integer> pair : map.entrySet()){ System.out.println(pair.getValue() + " " + pair.getKey()); }

Agata

Level 20 , Warsaw, Poland

29 April 2020, 14:22

Thanks for keeping up with me this far :) I saw that for others "if" worked with only "is.Empty()" condition so I don't know why I get a NullPointer while using if(s.isEmpty()){} Still can't initialize immediately and now it looks like this: while(true){ String s = reader.readLine(); if ((s==null) || (s.equals(""))){ break; } int id = Integer.parseInt(s); String name = reader.readLine(); if ((name==null) || (name.equals(""))){ map.put(name, id); break; } map.put(name, id); } for(Map.Entry<String, Integer> pair : map.entrySet()){ System.out.println(pair.getValue() + " " + pair.getKey()); } while(true){ String s = reader.readLine(); if ((s==null) || (s.equals(""))){ break; } int id = Integer.parseInt(s); String name = reader.readLine(); if ((name==null) || (name.equals(""))){ map.put(name, id); break; } map.put(name, id); } for(Map.Entry<String, Integer> pair : map.entrySet()){ System.out.println(pair.getValue() + " " + pair.getKey()); }

Agata

Level 20 , Warsaw, Poland

29 April 2020, 14:23

two times the same code unintentionally

Stefan Maric

Level 22 , Frankfurt , Germany

29 April 2020, 15:32

Try removing (s == null) condition in your if, only second condition will be enough. Change your hashMap printing loop to this: for(Map.Entry<String, Integer> pair : map.entrySet()) { String key = pair.getKey(); int value = pair.getValue(); System.out.println(value + " " + key); }

Agata

Level 20 , Warsaw, Poland

29 April 2020, 16:00

It gives NullPointer while(true){ String s = reader.readLine(); if (s.equals("")){ break; } int id = Integer.parseInt(s); String name = reader.readLine(); if ((name==null) || (name.equals(""))){ map.put(name, id); break; } map.put(name, id); } for(Map.Entry<String, Integer> pair : map.entrySet()){ String key = pair.getKey(); int value = pair.getValue(); System.out.println(value + " " + key); }

Stefan Maric

Level 22 , Frankfurt , Germany

29 April 2020, 16:24

Both IF statements need to be same. Only one condition is enough. Second If is : if (name.equals("")) {.....} Change your second if and it should be ok. Rest of the code is ok.

Agata

Level 20 , Warsaw, Poland

29 April 2020, 16:50

Still NullPointer :(

Stefan Maric

Level 22 , Frankfurt , Germany

29 April 2020, 17:09

Reset your task and enter this: while (true) { String value = reader.readLine(); if (value.equals("")) { break; } int id = Integer.parseInt(value); String name = reader.readLine(); if (name.equals("")) { map.put(name, id); break; } map.put(name, id); } for (Map.Entry<String, Integer> pair : map.entrySet()) { String key = pair.getKey(); int value = pair.getValue(); System.out.println(value + " " + key); } I got correct output with this.

Agata

Level 20 , Warsaw, Poland

29 April 2020, 17:17

I literally copy past and still have a NullPointer... Mabe you have something more than import java.io.*; and import java.util.*;?

Stefan Maric

Level 22 , Frankfurt , Germany

29 April 2020, 17:29

import java.io.*; import java.util.HashMap; import java.util.Iterator; import java.util.Map; public class Solution { public static void main(String[] args) throws IOException { BufferedReader reader = new BufferedReader(new InputStreamReader(System.in)); HashMap<String, Integer> map = new HashMap<String, Integer>(); while (true) { String value = reader.readLine(); if (value.equals("")) { break; } int id = Integer.parseInt(value); String name = reader.readLine(); if (name.equals("")) { map.put(name, id); break; } map.put(name, id); } for (Map.Entry<String, Integer> pair : map.entrySet()) { String key = pair.getKey(); int value = pair.getValue(); System.out.println(value + " " + key); } } } This is my complete task. try this.