jude jude - 24 days ago 8
Java Question

Java Array of user defined type

I'm trying to populate an array of user-defined type - composite of 3 Strings, and 1 Boolean. The type name is

PrinterType.
with methods to SET and GET for these 3 Strings and Boolean values.

I'm trying to use it in another class file where array population will be executed but when I run the project, I'm getting
java.lang.NullPointerException
.

I understand that this is a problem of string Field not initialized but I don't know how to initialize the String fields of a user-defined-type array. I hope somebody can help me on this. The user defined type and implementing classes are below.

by the way, error points to line of implementing class:
Printers[i].setPersonality(aLineOfText[0].toString());


//implementing class =======================================
package MainPkg;

import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;

public class ReadDefinitions
{
final String sFileName = "C:/Definitions OEvP/Printers.txt";
private static int iNoOfLines;
public PrinterType[] Printers;


private int getNumberOfLines() throws IOException
{
FileReader fr = new FileReader(sFileName);
BufferedReader br = new BufferedReader(fr);

iNoOfLines = 0;

while (br.readLine() != null)
{
iNoOfLines++;
}

br.close();
fr.close();

return iNoOfLines;
}

public void setArray() throws IOException
{
Printers = new PrinterType[this.getNumberOfLines()];
int i = 0;

FileReader fr = new FileReader(sFileName);
BufferedReader br = new BufferedReader(fr);
String[] aLineOfText = {};

while (i != this.getNumberOfLines())
{
aLineOfText = br.readLine().split(";");
Printers[i].setPersonality(aLineOfText[0].toString());
Printers[i].setProductNumber(aLineOfText[1].toString());
Printers[i].setPL(aLineOfText[2].toString());

if ("1" == aLineOfText[3].toString())
{
Printers[i].setHipot(Boolean.TRUE);
}
else
{
Printers[i].setHipot(Boolean.FALSE);
}

i++;
aLineOfText = null;
System.gc();
}
}

}


//user defined Class ======================================

package MainPkg;

public class PrinterType
{
private String sPersonality;
private String sProductNumber;
private String sPL;
private Boolean bHipot;

//constructor
PrinterType()
{
sPersonality = "test";
sProductNumber = "test";
sPL = "test";
}

//printer information
//set methods
public void setPersonality(String localString)
{
sPersonality = localString;
}

public void setProductNumber(String localString)
{
sProductNumber = localString;
}

public void setPL(String localString)
{
sPL = localString;
}

public void setHipot(Boolean localBoolean)
{
bHipot = localBoolean;
}

//get methods
public String getPersonality()
{
return sPersonality;
}

public String getProductNumber()
{
return sProductNumber;
}

public String getPL()
{
return sPL;
}

public Boolean getHipot()
{
return bHipot;
}
}

Answer

You are not initializing the items of your Printer array.

You are just making an array of null items of PrinterType.

Printers = new PrinterType[this.getNumberOfLines()];

// Initialization
for(int i = 0, l = this.getNumberOfLines(); i < l; i++)
    Printers[i] = new PrinterType();