用户定义类型的 Java 数组

Question

我正在尝试填充用户定义类型的数组 - 由 3 个字符串和 1 个 boolean 值组成的数组。类型名称为 PrinterType.，并提供这 3 个字符串和 boolean 值的 SET 和 GET 方法。

我试图在另一个类文件中使用它，其中将执行数组填充，但是当我运行该项目时，我收到 java.lang.NullPointerException。

我知道这是字符串字段未初始化的问题，但我不知道如何初始化用户定义类型数组的字符串字段。我希望有人能在这方面帮助我。用户定义的类型和实现类如下。

顺便说一句，错误指向实现类的行: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 1

您没有初始化打印机阵列的项目。

您只是创建了一个包含 PrinterType 空项的数组。

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

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