for循环中超出范围的异常打印小于Java中的arraylist大小

Question

even though I clearly specify in the for loop that I want it to print until arraylist.size, the terminal returns an OutOfBounds Exception

public static void PrintPlayList() {
        int lengthsongs = songs.size();
        int lengthadds = adds.size();
        int amountadds = 0;

    for (int i = 0; i < lengthsongs; i++) {
        playlist.add(songs.get(i));
        if (amountadds < lengthadds) {
            playlist.add(adds.get(amountadds));
            amountadds++;
        }
    }

    int lengthplaylist = playlist.size();
    for (int i = 0; i < lengthplaylist; i++) {
        System.out.println(songs.get(i).toString());
        System.out.println(adds.get(i).toString());
    }
}

And this is what the compiler returns: How is it possible? How can I fix it?

java.lang.IndexOutOfBoundsException: Index: 18, Size: 18
    at java.util.ArrayList.rangeCheck(Unknown Source)
    at java.util.ArrayList.get(Unknown Source)
    at Main.PrintPlayList(Main.java:153)
    at Main.Interface(Main.java:55)
    at Main.main(Main.java:34)

Answer 1

If you use a debugger, you should see that the playlist has more elements than either songs or adds as it is the sum of these (though not quite) This error is produced at runtime not compile time.

The simplest solution is

public static void printPlayList() {
    playlist.clear();
    playlist.addAll(songs);
    playlist.addAll(adds);
    playlist.forEach(System.out::println);
}

or just

public static void printPlayList() {
    songs.forEach(System.out::println);
    adds.forEach(System.out::println);
}

Answer 2

I think the problem is here:

for (int i = 0; i < lengthplaylist; i++) {
        System.out.println(songs.get(i).toString());
        System.out.println(adds.get(i).toString());
    }

lengthplaylist can be larger then lengthsongs in your code. And you're using for loop to go from 0 to lengthplaylist instead of lengthsongs .

You should also give attention to adds.get(i).toString() because for this to execute all the lengths must be same.

You may just use different variables in your loop for them like this:

for (int i = 0,j=0; i < lengthsongs && j<lengthadds; i++,j++) {
        System.out.println(songs.get(i).toString());
        System.out.println(adds.get(j).toString());
}

Answer 3

The list playlist is not initialized inside PrintPlayList() , so it might contain elements before.
In this loop:

for (int i = 0; i < lengthsongs; i++) {
    playlist.add(songs.get(i));
    if (amountadds < lengthadds) {
        playlist.add(adds.get(amountadds));
        amountadds++;
    }
}

you add all elements of songs to playlist , so playlist has at least as many elements as songs , but does it contain more? I don't know but you can find out by debugging.
The same applies to the list adds .
Do they all have the same size? This loop:

for (int i = 0; i < lengthplaylist; i++) {
    System.out.println(songs.get(i).toString());
    System.out.println(adds.get(i).toString());
}

will succeed if they do have the same size or playlist 's size is less than the other 2 lists.

Answer 4

ArrayList in Java is indexed from 0. You are accessing index 18, however your list is contains elements from 0 to 17.

Since you store your songs and adds in playlists , you can print them directly from the playlist like this:

for (int i = 0; i < lengthplaylist; i++) {
    System.out.println(playlist.get(i).toString());
}