如何在Java中将ArrayList元素存储到Array中？

Question

I am new to Java and was wondering if anyone would help me out with the logic below. What am trying to do is to iterate over a list and store each list element into Array. Once that's done, then I want to check the array element for correct answers. So for example 3,2,1 is enter then the final score should be 3. Here is the code.

Code

import java.rmi.RemoteException;
import java.util.ArrayList;
import java.util.List;

public class IterateOverArray {

public static int SCORE = 0;
static List<Integer> list = new ArrayList<Integer>();
static int[] temp;
public static void main(String[] args) throws Exception {

    list.clear();
    list.add(3);
    list.add(2);
    list.add(1);
    getScore();
}

public static void getScore() throws RemoteException {

    temp = new int[3];

    for (Integer value : list) {
        for (int i = 0; i < temp.length; i++) {
            temp[i] += value.intValue();
        }
        if (temp[0] == 3) {
            SCORE++;
        }
        if (temp[1] == 2) {
            SCORE++;
        }
        if (temp[2] == 1) {
            SCORE++;
        }
    }
    System.out.println("total score: " + SCORE); // Final Score should be 3!
}
}

Many Thanks!

Answer 1

When in doubt with an algorithm: Mental Step-through!

1. call getScore()
2. new array tmp , all elements initialized to 0
3. first iteration, value of value is 3
4. add 3 to all elements in the array (makes all of them 3)
5. check if first element in array is 3 --> it is, increase Score
6. next iteration, value of value is now 2
7. add 2 to all Elements of the array (makes all of them 5 )
8. ...

You see your flaw here?

The values in tmp will grow higher, and will then never evaluate to true in your if -statements. Did you want to use = instead of += in your inner for-loop?

---

Here is a sample-implementation:

static List<Integer> list = new ArrayList<Integer>();
// ...
list.add(3);
list.add(2);
list.add(1);
getScore();

public static void getScore() throws RemoteException {
    if (list.get(0) == 3) {
        SCORE++;
    }
    if (list.get(1) == 2) {
        SCORE++;
    }
    if (list.get(2) == 1) {
        SCORE++;
    }
    System.out.println("total score: " + SCORE);
}

A List is just a dynamically growing array. It behaves just like an array and you can get a single item from it by using the get(index) -method (which is the "equivalent" to using [index] ).

You don't need to copy your contents, at all. But if you must use an array, you can convert a List to an array by using the List.toArray() -method .

Answer 2

I'd just put the correct answers in an array, and compare them as you go. No need to transform things into arrays and whatnot.

int getScore(List<Integer> answers) {
    Integer[] correctAnswers = {3,2,1};
    int score = 0;
    for (int i = 0; i < 3; i++) 
        if (correnctAnswers[i].equals(answers.get(i)))
            score++;
    return score;
}

Answer 3

package farzi;

import java.util.ArrayList;

public class ArrayListToArray 
{
    public static void main (String args[])
    {
        ArrayList<String> arrList = new ArrayList<String>();
        arrList.add("hussi1");
        arrList.add("hussi2");
        arrList.add("hussi3");
        String[] strArray = new String[arrList.size()];
        arrList.toArray(strArray);
        for(int i=0;i<strArray.length;i++)
        {
            System.out.println(strArray[i]);
        }
    }

}