Why the all exceptions were not added to my Arraylist

Pytania dotyczące zadania

Charting our own course

Wielowątkowość w Java, Poziom 5, Lekcja 9

Rozwiązane

I don't know why the first exception did not want to be added to my Arraylist?

Implement the UncaughtExceptionHandler interface in the Solution class, which must:
1. Interrupt the thread that threw the exception.
2. Display the exception's stack trace, starting with the innermost exception.

new Exception("ABC", new RuntimeException("DEF", new IllegalAccessException("GHI"))) Example output: java.lang.IllegalAccessException: GHI java.lang.RuntimeException: DEF java.lang.Exception: ABC

Wymagania:

The Solution class must implement the Thread.UncaughtExceptionHandler interface.
After calling uncaughtException(), you must interrupt the thread that threw the exception.
Then display the exception stack trace, starting with the innermost exception.
Messages should be displayed in this format: "<exception class>: <exception message>".

package com.codegym.task.task25.task2512; /* Charting our own course */ import java.sql.SQLOutput; import java.util.ArrayList; import java.util.LinkedList; import java.util.Stack; public class Solution implements Thread.UncaughtExceptionHandler { @Override public void uncaughtException(Thread t, Throwable e) { //Why we use here interupt? t.interrupt(); //Creating Arraylist to add all created exceptions ArrayList<Throwable> list = new ArrayList<Throwable>(); //Getting the first exception Throwable ie = e.getCause(); while (ie != null){ list.add(ie); //asking for the next exception on the Stack trace? ie = ie.getCause(); } for (int i = list.size()-1; i >=0; i--) { System.out.println(list.get(i).getClass().getName() +":"+list.get(i).getMessage()); } } public static void main(String[] args) throws Exception { Solution s = new Solution(); Thread.currentThread().setDefaultUncaughtExceptionHandler(s); throw new Exception("ABC", new RuntimeException("DEF", new IllegalAccessException("GHI"))); } }

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Guadalupe Gagnon

Poziom 37 , Tampa, United States

21 lipca 2022, 19:41

rozwiązanie

The problem is that getCause() returns the next Throwable. In what you have to test you have three throwables named "ABC", "DEF", and "GHI". The very first one, "ABC", is passed into the method. When .getCause() is called it returns the next one, which is "DEF"; and then finally "GHI" is returned with the next call. The problem is that e.getCause() is added to the list first, however just simply 'e' is never added. Now regarding output, take a look here:

java.lang.IllegalAccessException: GHI  //← this is what is expected by the task
java.lang.IllegalAccessException:GHI  // ← this is what the this code outputs

your output line is missing one space, however it is also too complicated imo as simply outputting a throwable is going to get you the format you are looking for:

// these two lines output the same thing
System.out.println(list.get(i).getClass().getName() +": "+list.get(i).getMessage());
System.out.println(list.get(i));

Tomek

Poziom 20 , Poland

Expert

21 lipca 2022, 20:19

Thank you a lot. It is very helpful advice. I did it in another way and finally it works :) .

@Override
public void uncaughtException(Thread t, Throwable e) {
    //Why we use here interupt?
    t.interrupt();
    //Creating Arraylist to add all created exceptions
    ArrayList<Throwable> list = new ArrayList<Throwable>();
    //Getting the first exception
    while (e!= null){
        list.add(e);
        //asking for the next exception on the Stack trace?
        e = e.getCause();
    }
    for (int i = list.size()-1; i >=0; i--) {
        System.out.println(list.get(i));
    }
}