Why am I getting "must be caught or declared to be thrown" on my program?

Question

I have been working on this program for quite sometime and my brain is fried. I could use some help from someone looking in.

I'm trying to make a program that reads a text file line by line and each line is made into an ArrayList so I can access each token. What am I doing wrong?

import java.util.*;
import java.util.ArrayList;
import java.io.*;
import java.rmi.server.UID;
import java.util.concurrent.atomic.AtomicInteger;

public class PCB {
    public void read (String [] args) {
        BufferedReader inputStream = null;

        try {
            inputStream = new BufferedReader(new FileReader("processes1.txt"));

            String l;
            while ((l = inputStream.readLine()) != null) {
                write(l);
            }
        }
        finally {
            if (inputStream != null) {
                inputStream.close();
            }
        }
    }

    public void write(String table) {
        char status;
        String name;
        int priority;

        ArrayList<String> tokens = new ArrayList<String>();

        Scanner tokenize = new Scanner(table);
        while (tokenize.hasNext()) {
            tokens.add(tokenize.next());
        }

        status = 'n';
        name = tokens.get(0);
        String priString = tokens.get(1);
        priority = Integer.parseInt(priString);

        AtomicInteger count = new AtomicInteger(0);
        count.incrementAndGet();
        int pid = count.get();

        System.out.println("PID: " + pid);
    }
}

I am about to poke out my eyeballs. I got three errors:

U:\Senior Year\CS451- Operating Systems\Project1 PCB\PCB.java:24: unreported exception java.io.IOException; must be caught or declared to be thrown
            inputStream.close();}
                             ^
U:\Senior Year\CS451- Operating Systems\Project1 PCB\PCB.java:15: unreported exception java.io.FileNotFoundException; must be caught or declared to be thrown
        inputStream = new BufferedReader(new FileReader("processes1.txt"));
                                         ^
U:\Senior Year\CS451- Operating Systems\Project1 PCB\PCB.java:18: unreported exception java.io.IOException; must be caught or declared to be thrown
        while ((l = inputStream.readLine()) != null) {
                                        ^

What am I doing wrong?

Answer 1

When you work with I/O in Java most of the time you have to handle IOException which can occur any time when you read/write or even close the stream.

You have to put your sensitive block in a try//catch block and handle the exception here.

For example:

try{
    // All your I/O operations
}
catch(IOException ioe){
    //Handle exception here, most of the time you will just log it.
}

---

Resources:

• oracle.com - Lesson: Exceptions

Answer 2

Java checks exception specifications at compile time. You must either catch the exception or declare it thrown in your method signature. Here's how you would declare that it may be thrown from your method:

   public void read (String [] args) throws java.io.IOException {

Catch the exception if your method needs to do something in response. Declare it as thrown if your caller needs to know about the failure.

These are not mutually exclusive. Sometimes it is useful to catch the exception, do something and re-throw the exception or a new exception that wraps the original (the "cause").

RuntimeException and its subclasses do not need to be declared.