FAQ

ArrayIndexOutOfBoundsException

Background

• An array has a fixed number of slots; the number of slot's is the arrays' length.
• In Java, arrays are zero-indexed; this means we start indexing the array at 0.

Explanation

• An index must satisfy the array's bounds $0 \leq i \leq (\texttt{array.length - 1})$.
  • We can also write the bounds as $0 \leq i < \texttt{array.length}$.
• An index that does not satisfy the bounds is "out of bounds."

Example

xxxxxx xxxxxx xxxxxx xxxxxx xxxxxx
foo[0] foo[1] foo[2] foo[3] foo[4]

• int[] foo = new int[5]; has length 5.
• We can index into the array with foo[0], foo[1], foo[2], foo[3], and foo[4].
• The only valid indexes into foo are 0, 1, 2, 3, and 4.
• foo[5] will throw an ArrayIndexOutOfBoundsException.
• foo[42] will throw an ArrayIndexOutOfBoundsException.
• foo[-1] will throw an ArrayIndexOutOfBoundsException.

How can I add sound?

import javax.sound.sampled.*;

//https://stackoverflow.com/questions/3780406/how-to-play-a-sound-alert-in-a-java-application
static class SoundUtils {

    public static float SAMPLE_RATE = 8000f;

    public static void init() {
        if (sdl != null) {
            sdl.drain();
            sdl.stop();
            sdl.close();
        }
        try {
            AudioFormat af = 
                new AudioFormat(
                        SAMPLE_RATE, // sampleRate
                        8,           // sampleSizeInBits
                        1,           // channels
                        true,        // signed
                        false);      // bigEndian
            sdl = AudioSystem.getSourceDataLine(af);
            sdl.open(af);
            sdl.start();
        } catch (Exception e) {}
    }

    public static void tone(int hz, int msecs) {
        tone(hz, msecs, 1.0);
    }

    static SourceDataLine sdl;

    public static void tone(int hz, int msecs, double vol) {
        byte[] buf = new byte[1];
        for (int i = 0; i < 8 * msecs; i++) {
            double angle = i / (SAMPLE_RATE / hz) * 2.0 * Math.PI;
            buf[0] = (byte)(Math.sin(angle) * 127.0 * vol);
            sdl.write(buf,0,1);
        }
    }
}