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Java Cookbook
book

Java Cookbook

by Ian F. Darwin
June 2001
Intermediate to advanced content levelIntermediate to advanced
888 pages
21h 1m
English
O'Reilly Media, Inc.
Content preview from Java Cookbook

Resizing an Array

Problem

The array filled up, and you got an ArrayIndexOutOfBoundsException .

Solution

Make the array bigger.

Discussion

One approach is to allocate the array at a reasonable size to begin with, but if you find yourself with more data than will fit, reallocate a new, bigger array and copy the elements into it.[22] Here is code that does so:

import java.util.*;
/** Re-allocate an array, bigger... */
public class Array2  {
    public static void main(String argv[]) {
        int nDates = 0;
        final int MAX = 10;
        Calendar dates[] = new Calendar[MAX];
        Calendar c;
        while ((c=getDate(  )) != null) {

            // if (nDates >= dates.length) {
            //     System.err.println("Too Many Dates! Simplify your life!!");
            //     System.exit(1);  // wimp out
            // }

            // better: reallocate, making data structure dynamic
            if (nDates >= dates.length) {
                Calendar tmp[] = new Calendar[dates.length + 10];
                System.arraycopy(dates, 0, tmp, 0, dates.length);
                dates = tmp;    // copies the array reference
                // old array will be garbage collected soon...
            }
            dates[nDates++] = c;
        }
        System.out.println("Array size = " + dates.length);
    }

    static int n;
    /* Dummy method to return a sequence of 21 Calendar references,
     * so the array should be sized >= 21.
     */
    public static Calendar getDate(  ) {
        if (n++ > 21)
            return null;
        return Calendar.getInstance(  );
    }
}

This technique will work reasonably well for simple linear collections of data. For data with a more variable structure, you will probably want to use a more dynamic approach, as in Section 7.4.

[22]

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Publisher Resources

ISBN: 0596001703Supplemental ContentCatalog PageErrata