Java

why null pointer exception?

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Join Date: May 2008

Posts: 33

Reputation: gotm is an unknown quantity at this point

Solved Threads: 0

gotm

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Light Poster

why null pointer exception?

May 1st, 2009

It keeps giving me this exception when it seems like I am adding a choice to my choices vector, and I don't know why.

Here is that snippet of code. If you need more I can provide it.

Thanks ahead of time.

 Help with Code Tags 
 java Syntax (Toggle Plain Text) 
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.Vector;
 
public class multipleChoice extends question
{
	public Vector<String> choices;
 
	public multipleChoice()
	{
		System.out.println("Please enter the text of your question: ");
		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
		try {
			String textIn = br.readLine();
			text = textIn;
			System.out.println("Please enter the answer of your question: ");
			BufferedReader br2 = new BufferedReader(new InputStreamReader(System.in));
			try {
				String AnsIn = br.readLine();
				answer = AnsIn;
				BufferedReader inStream = new BufferedReader (
                        new InputStreamReader(System.in)
                    );
						System.out.println("Enter the number of choices: ");
						String inLine = inStream.readLine();
						int numChoices = Integer.parseInt(inLine);
						for (int j = 0; j < numChoices - 1; j++) {
							System.out.println("Please enter choice number " + (j + 1) + ": ");
							BufferedReader br3 = new BufferedReader(new InputStreamReader(System.in));
							try {
								String choice= br.readLine();
								choices.add(choice);
							} catch (IOException e) {
								e.printStackTrace();
							}	
						}
			} catch (IOException e) {
				e.printStackTrace();
			}
		} catch (IOException e) {
			e.printStackTrace();
		}
	}
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.Vector;

public class multipleChoice extends question
{
	public Vector<String> choices;
	
	public multipleChoice()
	{
		System.out.println("Please enter the text of your question: ");
		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
		try {
			String textIn = br.readLine();
			text = textIn;
			System.out.println("Please enter the answer of your question: ");
			BufferedReader br2 = new BufferedReader(new InputStreamReader(System.in));
			try {
				String AnsIn = br.readLine();
				answer = AnsIn;
				BufferedReader inStream = new BufferedReader (
                        new InputStreamReader(System.in)
                    );
						System.out.println("Enter the number of choices: ");
						String inLine = inStream.readLine();
						int numChoices = Integer.parseInt(inLine);
						for (int j = 0; j < numChoices - 1; j++) {
							System.out.println("Please enter choice number " + (j + 1) + ": ");
							BufferedReader br3 = new BufferedReader(new InputStreamReader(System.in));
							try {
								String choice= br.readLine();
								choices.add(choice);
							} catch (IOException e) {
								e.printStackTrace();
							}	
						}
			} catch (IOException e) {
				e.printStackTrace();
			}
		} catch (IOException e) {
			e.printStackTrace();
		}
	}

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Join Date: May 2009

Posts: 34

Reputation: Zibo is an unknown quantity at this point

Solved Threads: 3

Zibo

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Light Poster

Re: why null pointer exception?

May 1st, 2009

It's because You didn't create an instance of Your 'choices' variable. You need to allocate a memory by adding a line (in constructor i.e.):

 Help with Code Tags 
 Java Syntax (Toggle Plain Text) 
choices = new Vector<String>();
choices = new Vector<String>();

Oh, and I think You don't have to catch 3 times still one type of exception one after another. Remove 2 of them leaving 1 big try, so it would be like:

 Help with Code Tags 
 Java Syntax (Toggle Plain Text) 
try
{    //  <-  here starts try
			String textIn = br.readLine();
			text = textIn;
			System.out.println("Please enter the answer of your question: ");
			BufferedReader br2 = new BufferedReader(new InputStreamReader(System.in));
 
				String AnsIn = br.readLine();
				answer = AnsIn;
				BufferedReader inStream = new BufferedReader (
                        new InputStreamReader(System.in)
                    );
						System.out.println("Enter the number of choices: ");
						String inLine = inStream.readLine();
						int numChoices = Integer.parseInt(inLine);
						for (int j = 0; j < numChoices - 1; j++) {
							System.out.println("Please enter choice number " + (j + 1) + ": ");
							BufferedReader br3 = new BufferedReader(new InputStreamReader(System.in));
 
								String choice= br.readLine();
								choices.add(choice);
							}	
						}
			}
 
		}       //   <-  here ends try
                          catch (IOException e) {
			e.printStackTrace();
		}
try
{    //  <-  here starts try
			String textIn = br.readLine();
			text = textIn;
			System.out.println("Please enter the answer of your question: ");
			BufferedReader br2 = new BufferedReader(new InputStreamReader(System.in));
			
				String AnsIn = br.readLine();
				answer = AnsIn;
				BufferedReader inStream = new BufferedReader (
                        new InputStreamReader(System.in)
                    );
						System.out.println("Enter the number of choices: ");
						String inLine = inStream.readLine();
						int numChoices = Integer.parseInt(inLine);
						for (int j = 0; j < numChoices - 1; j++) {
							System.out.println("Please enter choice number " + (j + 1) + ": ");
							BufferedReader br3 = new BufferedReader(new InputStreamReader(System.in));
							
								String choice= br.readLine();
								choices.add(choice);
							}	
						}
			}
                         
		}       //   <-  here ends try
                          catch (IOException e) {
			e.printStackTrace();
		}