Reading integer and string from console

Question

I implemented two Hashtable as shown below.

HashMap<Integer,String> streetno=new HashMap<Integer,String>();
   streetno.put(1, "Sachin Tendulkar");
   streetno.put(2, "Dravid");
   streetno.put(3,"Sehwag");
   streetno.put(4,"Laxman");
   streetno.put(5,"Kohli");


HashMap<String,Integer> streetname=new HashMap<String,Integer>();
   streetname.put("Sachin Tendulkar",1);
   streetname.put("Dravid",2);
   streetname.put("Sehwag",3);
   streetname.put("Laxman",4);
   streetname.put("Kohli",5);
   Iterator itr=streetno.keySet().iterator();

Now I'm asking user for input. If he enters the integer I want to retrieve particular value from the 1st hash table and if user enter the string I want to read the particular integer from 2nd hashtable.

My question is "How can I read the input from the user??" Because I don't know whether user enters the integer or string?? And I also wanted to know Can I retrieve particular value using Iterator depending on the key??

Peter Lawrey · Accepted Answer · 2011-12-29 16:18:07Z

1

How can I read the input from the user??

Something like

String line = scanner.nextLine();

Because I don't know whether user enters the integer or string??

Try to convert it to an integer

try {
  int num = Integer.parseInt(line);
  // lookup by number

} catch(NumberFormatException ignored) {
  // lookup by string

}

Can I retrieve particular value using Iterator depending on the key??

An Iterator is for iterating, a Map is for looking up by key.

answered Dec 29, 2011 at 16:18

Peter Lawrey

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Comments

Tomas Narros · Accepted Answer · 2011-12-29 16:35:37Z

First, you'll need to read the standard input. Handle it first as a String, to simplify.

   Scanner scanner=new Scanner(System.in);
   String userInput=scanner.nextLine();

Then, try to convert the String to an Integer. If the user typed a number, you'll get the key a the first Map, otherwise, you can asume it's a String key for the second one:

   String sName;
   Integer iNumber;
   try {
       iNumber=Integer.parseInt(userInput);
       //user intruduced a number, so get the streename
       sName=streetno.get(iNumber);

   } catch (NumberFormatException e) {
       //user introduced a not-numeric String, so get the streetnumber
       sName=userInput;
       iNumber=streetname.get(sName);
   }

You don't need to iterate over the keyset, as the Map.get() method will return you the corresponding value.

finally, don't forget to release the scanner (better in a finally block):

scanner.close();

Vaandu · Accepted Answer · 2011-12-29 16:40:47Z

You can read the input as mentioned in other answers. I just tried the main logic in this way. If combining two maps can be done, you can try this way.

            String input = "Laxman";            
            HashMap<String, String> street = new HashMap<String, String>();
            street.put("1", "Sachin Tendulkar");
            street.put("2", "Dravid");
            street.put("3", "Sehwag");
            street.put("4", "Laxman");         

            for (Map.Entry<String, String> entry : street.entrySet()) { 
                System.out.println("Key = " + entry.getKey() + ", Value = " + entry.getValue());
                if (input.equals(entry.getKey())) {
                    System.out.println(entry.getValue());   
                    break;
                } else if (input.equals(entry.getValue())) {
                    System.out.println(entry.getKey());   
                    break;
                }               
            }

javamonkey79 · Accepted Answer · 2011-12-29 16:17:22Z

0

I believe you'll need to use Integer.parseInt to figure out whether the input is and integer or not.

Unfortunately, there isn't really a "tryParse" or something like that in java, so you'll have to just catch the exception. You could use a regex to check whether it is numeric or not, but this might be more hassle than it is worth.

As far as reading in from the console, I would use:

Scanner console = new Scanner( System.in );

answered Dec 29, 2011 at 16:17

javamonkey79

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Comments

Scott Hunter · Accepted Answer · 2011-12-29 16:17:29Z

0

Read the input as a string; if it can be parsed as an Integer, use streetno, otherwise use streetname.

answered Dec 29, 2011 at 16:17

Scott Hunter

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Comments

Mechkov · Accepted Answer · 2011-12-29 16:18:19Z

0

You can use the Scanner class to retrieve user input. It has several useful methods like nextInt() or nextLine() which can be used to your advantage to determine if a user has entered an int or a string.

You can also make the user "say" what they are entering beforehand - int or string. But this is not very user friendly.

To get a value from a HashMap use the get(key) method, when providing the key.

answered Dec 29, 2011 at 16:18

Mechkov

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