Printing hashmap

[Donielle Locke-Bowen]

For our homework assignment, we have to write a program that reads integers from a specified file. If there are duplicate entries, we need to output them as well as they're locations. If not, we need to state that there aren't any duplicates. I've gotten most of the code below:

import java.lang.*;
import java.io.*;
import java.util.*;

public class Duplicate4
{
public static void duplicate4 (String filename) throws IOException
{
Scanner scan = new Scanner(filename);
Map<Integer,Integer> m = new HashMap<Integer,Integer>();

while(scan.hasNextInt())
	{
	int x = scan.nextInt();
	if(m.get(x) != null) m.put(x, m.get(x)+1);
	
	else{m.put(x,1);
	}
}
}
public static void main(String arg[]) throws IOException
	{
	duplicate4("assignment.txt");
	}
	
} 

The program compiles fine, but when I run it, needless to say nothing outputs - there's no println. I have no clue how to actually print the results. Everytime I add a println I get a compiling error. What's the syntax for printing Hashmaps? HELP!!!

[Henry Wong]

Everytime I add a println I get a compiling error.

It may be a good idea to start with what have you tried -- if you tell us, along with the error, we can tell you what you are doing wrong.

Henry

[Donielle Locke-Bowen]

Here's my code. Everything I've added has comment lines next to it. I added and removed each line when one wouldn't work.

import java.lang.*;   
import java.io.*;   
import java.util.*;   
  
public class Duplicate4   
{   
public static void duplicate4 (String filename) throws IOException   
{   
Scanner scan = new Scanner(filename);   
Map<Integer,Integer> m = new HashMap<Integer,Integer>();   
  
while(scan.hasNextInt())   
    {   
    int x = scan.nextInt();   
    if(m.get(x) != null) m.put(x, m.get(x)+1);   
       
    else{m.put(x,1);
   System.out.println(m.get(x))   //this actually compiles but again, the output is blank at runtime.
   System.out.println(m.put(x))  //compiler error
}   
}   
}   
public static void main(String arg[]) throws IOException   
    {   
    duplicate4("assignment.txt");   
    }   
       
}   

I've even done printCollection and printMap. Both have come back with compiler errors.

[Henry Wong]

System.out.println(m.put(x))

This won't compile. There is no put() method that takes one parameter.

I've even done printCollection and printMap. Both have come back with compiler errors.

Not enough details. What do you mean you "done printCollection and printMap"? And what compile errors?

Henry

[Donielle Locke-Bowen]

printCollection(x);
printCollection(scan);
printCollection(Map);
printCollection(HashMap);
printMap(x);
printMap(scan);
printMap(Map);
printMap(HashMap);

I've added all of these and have gotten "cannot find symbol"

I've never compiled complex java assignments like this, please be patient with me. Thank you.

[Henry Wong]

Donielle Locke-Bowen wrote:
I've added all of these and have gotten "cannot find symbol"

Did you create those methods? Those methods don't exist in the API, so you if want them, you'll have to create them first.

Henry

[Donielle Locke-Bowen]

Henry Wong wrote:

Donielle Locke-Bowen wrote:
I've added all of these and have gotten "cannot find symbol"

Did you create those methods? Those methods don't exist in the API, so you if want them, you'll have to create them first.

Henry

I just looked at examples from my textbook, which used both printMap and printCollection. Clearly I'm on the wrong track. I need serious help with this. I have no clue where to go from here.

[Henry Wong]

I just looked at examples from my textbook, which used both printMap and printCollection.

Book examples generally don't use stuff that doesn't exist. So, are these methods presented in earlier chapters? Or are the methods for the examples available for download somewhere?

Henry

[Stefan Brandenberger]

Donielle Locke-Bowen wrote:What's the syntax for printing Hashmaps? HELP!!!

Hi Donielle

System.out.println(m);

would do that for you.

But thats not what you really want .

You build a Map with the found integers as key and the number of their occurences as value. So, when you're finished with building the map, you have to loop over it (hint: Map.entrySet()) and print those keys with an associated value > 1. But maybe your textbook has examples for that.

Further: Your Scanner takes a String as constructor-argument. So what you actually are scanning is the string "assignment.txt" and not the content of a file with that name. Fortunately there's also a constructor that takes an InputStream. So all you have to do is first create a FileInputStream on your "assignment.txt"-file.

Stefan

[Campbell Ritchie]

And welcome to JavaRanch

[Donielle Locke-Bowen]

Hi Donielle

System.out.println(m);

would do that for you.

But thats not what you really want .

You build a Map with the found integers as key and the number of their occurences as value. So, when you're finished with building the map, you have to loop over it (hint: Map.entrySet()) and print those keys with an associated value > 1. But maybe your textbook has examples for that.

Further: Your Scanner takes a String as constructor-argument. So what you actually are scanning is the string "assignment.txt" and not the content of a file with that name. Fortunately there's also a constructor that takes an InputStream. So all you have to do is first create a FileInputStream on your "assignment.txt"-file.

Stefan

Here's my new code:

import java.lang.*;
import java.io.*;
import java.util.*;

public class Duplicate4
{
public static void duplicate4 (String filename) throws IOException
{
InputStream myFileStream = new FileInputStream (filename);

Map<Integer,Integer> m = new HashMap<Integer,Integer>();

while(myFileStream.hasNextInt())
	{
int x = myFileStream.nextInt();
if(m.get(x) != null) m.put(x, m.get(x)+1);
	
else{m.put(x,1);
for (Map.Entry<Integer,Integer> entry : m.entrySet()) {
System.out.println(entry.getKey() + " occured " + entry.getValue() + " times.");
}


}

}
}
public static void main(String arg[]) throws IOException
	{
	duplicate4("partTwo1.txt");
	}

Now I'm getting this:
Duplicate4.java:15: cannot find symbol
symbol : method hasNextInt()
location: class java.io.InputStream
while(myFileStream.hasNextInt())

[Campbell Ritchie]

The hasNextInt() method belongs to the Scanner class not the input stream class.

There is an example quite similar to what you want near the beginning of the Scanner class in the API documentation.