气泡排序arraylis不起作用

Question

I'm trying to bubble sort car make and year, where I would have the car year sorted and if two car makes are in the same year, then they are sorted alphabetically. My program works up to the point where I call BubbleSorted(). It's giving me an error java.lang.IndexOutOfBoundsException: Index: 0, Size: 0 and I don't know why. My program seems to be correct. Below is my program. I have 3 classes(main, bubblesortCars, GetCarInfo).

import java.util.ArrayList;
import java.util.Scanner;
import java.util.StringTokenizer;
import java.io.BufferedReader;
import java.io.FileReader;


public class TheMain {

    public static void main(String[] args) {

        Scanner keyboard=new Scanner(System.in);
        int choice;
        boolean done = false;

        try{
            String filename1 = "Demo.txt";
            FileReader inputFile = new FileReader(filename1);

            //Instantiate the BufferedReader Class
            BufferedReader bufferReader = new BufferedReader(inputFile);
            ArrayList<GetCarInfo> CarList = new ArrayList();

            //Variable to hold the one line data
            String line;
            StringTokenizer st;
            int i=0;

            // Read file line by line and print on the console
            while ((line = bufferReader.readLine()) != null)   {
                st = new StringTokenizer(line, "\t");
                st.nextToken();
                st.nextToken();
                String getMake = st.nextToken();
                st.nextToken();
                int getYear = Integer.parseInt(st.nextToken());
                GetCarInfo temp;
                temp = new GetCarInfo(getMake, getYear);
                CarList.add(temp);
            }
            bufferReader.close();



                      BubbleSortCars Sorted = new BubbleSortCars();
                         Sorted.bubblesorted(CarList, 0, CarList.size());


        }
        catch (Exception e) 
        { 
             e.printStackTrace();
        }

    }

}



import java.util.ArrayList;


public class BubbleSortCars {
    ArrayList <GetCarInfo> temp= new ArrayList();


    public void bubblesorted(ArrayList <GetCarInfo> grabber, int began, int end){

        for(int i =0; i<end-began-1; i++){
            for(int j=began; j<(end-i-1); j++){
                if(grabber.get(j).year > grabber.get(j+1).year){
                    temp.set(j, grabber.get(j));
                    grabber.set(j,grabber.get(j+1));
                    grabber.set(j+1, temp.get(j));
                    System.out.println("Success"); 
                } 
                else if(grabber.get(j).year==grabber.get(j+1).year){
                    if((grabber.get(j).make).compareTo(grabber.get(j+1).make)>0){
                        temp.set(j, grabber.get(j));
                        grabber.set(j, grabber.get(j+1));
                        grabber.set(j+1, temp.get(j));
                        System.out.println("Success");
                    }
                }
            }
        } 
    }
}




public class GetCarInfo {
    int year;
    String make;

    public GetCarInfo(String newmake, int newyear){
        make = newmake;
        year = newyear;
    }
}

Answer 1

Reason you get IndeOutOfBoundException is due to this line:

temp.set(j, grabber.get(j));

and your definition of arrayList.

 ArrayList<GetCarInfo> temp = new ArrayList();

Here you are defining temp as arrayList without any element and you are trying to set an element at 0th location which is not defined. See this for your reference http://docs.oracle.com/javase/7/docs/api/java/util/ArrayList.html#set%28int,%20E%29

When you define temp as above it created with size 0 and jdk does check internally if index that you are trying to access is less than size then only it will allow you to access/set content.

So one way to avoid this, you define your temp arrayList in your method like:

ArrayList<GetCarInfo> temp = new ArrayList(grabber);

Or you could use grabber arrayList to do the sorting without any other data structure.

Answer 2

The problem is with the ArrayList temp . Please refer the Oracle documentation for the set method.

Here you don't need an ArrayList. User a simple GetCarInfo object as temp variable.