Java: tricky array (For me anyway!)

youcancallmeal · 29-11-2007 04:21PM #1

Hey all I'm very new to Java and I'm having trouble with arrays. I can do basic arrays where I can display an index against a value. I have this particular program that displays distances between cities. I have got it work using nested if blocks but I want to get it to work using arrays. I'm not sure even where to start and the crappy Deitel&Deitel book I'm sure a lot of you are aware of is no help.

Heres the original table I had to work with:

This is how I got it to work using nested if blocks.

import java.util.Scanner;

public class Destination
  
{

  private int destinationLocation;
  private int origin;
    
  public Destination()
  {}
  
  public void setDestinationLocation(int destLo)  
    { 
      destinationLocation = destLo;
    }         

    public int getDestinationLocation()
    {
      return destinationLocation;
    }

  public void setOrigin(int ogn)  
    { 
      origin = ogn;
    }         

  public int getOrigin()
    {
      return origin;
    }
    
  public void determineDistance()
    
  {
     Scanner input = new Scanner( System.in );
     
     System.out.print("Please select the origin of your trip: \n1. Belfast \n2. Cork \n3. Dublin \n4. Galway \n5. Limerick\n");
       origin=input.nextInt();
     
     System.out.print("Please select the destination of your trip: \n1. Belfast \n2. Cork \n3. Dublin \n4. Galway \n5. Limerick\n");
       destinationLocation=input.nextInt();
 
     if ( origin == 1 )
     {
      if ( destinationLocation == 2)
      System.out.println( "The distance between Belfast and Cork is 300 Kilometers"); 
      if ( destinationLocation == 3)
      System.out.println( "The distance between Belfast and Dublin is 150 Kilometers");
      if ( destinationLocation == 4)
      System.out.println( "The distance between Belfast and Galway is 200 Kilometers");
      if ( destinationLocation == 5)
      System.out.println( "The distance between Belfast and Limerick is 300 Kilometers");
     }  
     
     else if (origin == 2)
     {
      if ( destinationLocation == 1)
      System.out.println( "The distance between Cork and Belfast is 300 Kilometers"); 
      if ( destinationLocation == 3)
      System.out.println( "The distance between Cork and Dublin is 256 Kilometers");
      if ( destinationLocation == 4)
      System.out.println( "The distance between Cork and Galway is 150 Kilometers");
      if ( destinationLocation == 5)
      System.out.println( "The distance between Cork and Limerick is 75 Kilometers");
     } 
     
     else if (origin == 3)
     {
      if ( destinationLocation == 1)
      System.out.println( "The distance between Dublin and Belfast is 150 Kilometers"); 
      if ( destinationLocation == 2)
      System.out.println( "The distance between Dublin and Cork is 256 Kilometers");
      if ( destinationLocation == 4)
      System.out.println( "The distance between Dublin and Galway is 180 Kilometers");
      if ( destinationLocation == 5)
      System.out.println( "The distance between Dublin and Limerick is 220 Kilometers");
     } 
     
     else if (origin == 4)
     {
      if ( destinationLocation == 1)
      System.out.println( "The distance between Galway and Belfast is 200 Kilometers"); 
      if ( destinationLocation == 2)
      System.out.println( "The distance between Galway and Cork is 150 Kilometers");
      if ( destinationLocation == 3)
      System.out.println( "The distance between Galway and Dublin is 180 Kilometers");
      if ( destinationLocation == 5)
      System.out.println( "The distance between Galway and Limerick is 134 Kilometers");
     }   
     
     else if (origin == 5)
     {
      if ( destinationLocation == 1)
      System.out.println( "The distance between Limerick and Belfast is 300 Kilometers"); 
      if ( destinationLocation == 2)
      System.out.println( "The distance between Limerick and Cork is 75 Kilometers");
      if ( destinationLocation == 3)
      System.out.println( "The distance between Limerick and Dublin is 220 Kilometers");
      if ( destinationLocation == 4)
      System.out.println( "The distance between Limerick and Galway is 134 Kilometers");
     }        
          
    else 
      System.out.println( "Valid numbers not entered please try again" );
        
  }
}

public class DestinationTest

{

  public static void main( String args[] )
    
  {
    
    Destination myDestination = new Destination();
    
    myDestination.determineDistance();
    
  }
  
}

Any pointers would be greatly appreciated

EL_Loco · 29-11-2007 04:51PM

that image won't load here at work but in general terms

you'll need a 2 dimensional array to replicate the table.
you'll need to populate the array with the data.
you'll need to ask the user the city, which will be a row in the array.
you'll need to ask the user the destination city, which will be a column.
These 2 "co-ordinates" should relate to a value in the 2D array which holds your answer.

Giblet · 29-11-2007 04:51PM

Make a 2D array;

int [][] distances = new int [origin][destinationLocation];

origin and destination being the number of rows and columns

so distances[0][1] would be 300; (origin 0 , destinationLocation 1)

You can use this to populate and retrieve data.

youcancallmeal · 29-11-2007 05:27PM

So would it be something like this:

Destination[][] destinations = new Destination [4][4];
       
destinations[0] = new Destination(300,150,200,300); //Belfast
destinations[1] = new Destination(300,256,150,75);  //Cork
destinations[2] = new Destination(150,256,180,220); //Dublin
destinations[3] = new Destination(200,150,180,134); //Galway
destinations[3] = new Destination(300,75,220,134);  //Limerick

I tried compiling it but I'm getting errors saying

cannot find symbol
symbol  : constructor Destination(int,int,int,int)
location: class Destination

EL_Loco · 29-11-2007 05:56PM

Destination[][] destinations = new Destination [4][4];

I think should be (based on above)

int[][] destinations = new Destination [4][4];

edit: I'm not sure about the way you're populating your array. but I found this code example which may help if you're having trouble:

String[][] names = {{"Mr. ", "Mrs. ", "Ms. "},
                            {"Smith", "Jones"}};

lynchie · 29-11-2007 05:59PM

youcancallme>al wrote: »
I tried compiling it but I'm getting errors saying
cannot find symbol
symbol  : constructor Destination(int,int,int,int)
location: class Destination

The compiler is telling you whats wrong... It cant find a constructor in class Destination that takes 4 parameters...

Hobbes · 30-11-2007 11:20AM

If it was me I would create a TreeMap and use the names vs as keys. Example.

Map<String, Integer> table = new TreeMap<String, Integer>(); 


table.put("Cork-Dublin",  256);
table.put("Belfast-Cork", 300);

// To get the value then. 

String from = "Cork";
String to = "Dublin";

int miles = table.get(from + "-" + to); // will get 256 miles.

This will auto-sort the values, stop duplicates and allow you to quicky retrieve the keys quickly to populate your rows. to make it cleaner just have the from/to transpose themselves if the key isn't found.

youcancallmeal · 07-12-2007 01:18PM

I left this for a while because it was wrecking my head. Anyway I came back to it and got it to work pretty quickly. Heres what I did:

import java.util.Scanner;

public class Destination1
  
{
  
  private int destinationLocation;
  private int origin;
  
  public Destination1()
  {}  
  
  public void setDestinationLocation(int destLo)  
    { 
      destinationLocation = destLo;
    }         

    public int getDestinationLocation()
    {
      return destinationLocation;
    }

  public void setOrigin(int ogn)  
    { 
      origin = ogn;
    }         

  public int getOrigin()
    {
      return origin;
    }

    
    
  public void determineDistance()
    
  {
     Scanner input = new Scanner( System.in );
     
     System.out.print("Please select the origin of your trip: \n1. Belfast \n2. Cork \n3. Dublin \n4. Galway \n5. Limerick\n");
       origin=input.nextInt();
     
     System.out.print("Please select the destination of your trip: \n1. Belfast \n2. Cork \n3. Dublin \n4. Galway \n5. Limerick\n");
       destinationLocation=input.nextInt();
    
    int distance[][] = new int[5][5];
    
    distance[0][0]=0;
    distance[0][1]=300;
    distance[0][2]=150;
    distance[0][3]=200;
    distance[0][4]=300;
    distance[1][0]=200;
    distance[1][1]=0;
    distance[1][2]=256;
    distance[1][3]=150;
    distance[1][4]=75;
    distance[2][0]=150;
    distance[2][1]=256;
    distance[2][2]=0;
    distance[2][3]=180;
    distance[2][4]=220;
    distance[3][0]=200;
    distance[3][1]=150;
    distance[3][2]=200;
    distance[3][3]=0;
    distance[3][4]=134;
    distance[4][0]=300;
    distance[4][1]=75;
    distance[4][2]=300;
    distance[4][3]=135;
    distance[4][4]=0;

    
    System.out.printf ("\nThe distance between those two locations is: %dkm", distance[origin - 1][destinationLocation - 1]);
      
  }
}

I don't think I needed the set and get methods for DestinationLocation and Origin but I put them in anyway just out of habit.

Hobbes · 07-12-2007 07:20PM

While I still think my last post is the more elegant way to do it. If you really have to code it that way I suggest you change the initialisation of the data like so.

int distance[][] = { 
	{ 0,   300, 150, 200, 300 }, 
	{ 200,   0, 256, 150,  75 }, 
	{ 150, 256,   0, 180, 220 },
	{ 200, 150, 200,   0, 134 },
	{ 300,  75, 300, 135,   0 }
	};

It will make your code much easier to read. I would also make the counties as Enums.

Java: tricky array (For me anyway!)

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