Why ArrayList capacity is not incremented according to it's formula in source code?

[Ganish Patil]

This is my program which I check in debug mode. I found capacity of ArrayList increasing in following manner mentioned in comments. I checked source code, where I found this formula
int newCapacity = (oldCapacity * 3)/2 + 1; in method public void ensureCapacity(int minCapacity) but why it is not incrementing according to this formula.

I found this link which says Till Java 6 int newCapacity = (oldCapacity * 3)/2 + 1; and (Update) From Java 7 int newCapacity = oldCapacity + (oldCapacity >> 1); but I'm using Java 8 still have this formula int newCapacity = (oldCapacity * 3)/2 + 1 is that website giving wrong information? or again they changed to older formula in Java 8? or I'm using older src.zip in Java 8 to get source code ? Below is code I used to check how it increases it's capacity

package arraylistexamples;

import java.util.ArrayList;

public class ArrayListInternalWorkingCheckDemo {

	ArrayList<String> myArrayListOne;

	public ArrayListInternalWorkingCheckDemo() {

		/*
		 * Formula int newCapacity = (oldCapacity * 3)/2 + 1;
		 */

		myArrayListOne = new ArrayList<String>();

		// Initial Capacity is 10 Ref: Source code
		myArrayListOne.add("A");
		myArrayListOne.add("A");
		myArrayListOne.add("A");
		myArrayListOne.add("A");
		myArrayListOne.add("A");
		myArrayListOne.add("A");
		myArrayListOne.add("A");
		myArrayListOne.add("A");
		myArrayListOne.add("A");
		myArrayListOne.add("A");
		myArrayListOne.add("A");

		// Now capacity became 15

		// 10 + 5 New Elements = 15
		myArrayListOne.add("A");
		myArrayListOne.add("A");
		myArrayListOne.add("A");
		myArrayListOne.add("A");
		myArrayListOne.add("A");

		// Now capacity became 22
		myArrayListOne.add("A");
		myArrayListOne.add("A");
		myArrayListOne.add("A");
		myArrayListOne.add("A");
		myArrayListOne.add("A");
		myArrayListOne.add("A");
		myArrayListOne.add("A");
		// Now capacity became 33

		myArrayListOne.add("A");
		myArrayListOne.add("A");
		myArrayListOne.add("A");
		myArrayListOne.add("A");
		myArrayListOne.add("A");
		myArrayListOne.add("A");
		myArrayListOne.add("A");
		myArrayListOne.add("A");
		myArrayListOne.add("A");
		myArrayListOne.add("A");
		myArrayListOne.add("A");
		// Now capacity became 48
	}

	public static void main(String[] args) {
		new ArrayListInternalWorkingCheckDemo();
	}
}

why it is increasing in this strange manner?

[Tim Moores]

According to its source code, Java 8 uses the same formula as Java 7, which would result in the sequence 10, 15, 22, 33 etc. that you observed. So it would seem that all is as it should be, no?

[Campbell Ritchie]

That shows the hazard of trying too hard to find out the internals of a class; you should leave implementation details well alone.
Does that mean that a 1‑element List is never enlarged? I tried it and the 1‑element List does seem to be enlarged.

[Ganish Patil]

Tim Moores wrote:According to its source code, Java 8 uses the same formula as Java 7

but on my system I have Java 8 but when clicked on myArrayListOne..ensureCapacity() method I get this

public void ensureCapacity(int minCapacity) {
	modCount++;
	int oldCapacity = elementData.length;
	if (minCapacity > oldCapacity) {
	    Object oldData[] = elementData;
	    int newCapacity = (oldCapacity * 3)/2 + 1;
    	    if (newCapacity < minCapacity)
		newCapacity = minCapacity;
            // minCapacity is usually close to size, so this is a win:
            elementData = Arrays.copyOf(elementData, newCapacity);
	}
    }

am I using older src.zip ? Because I got that from my colleague. This is the information found in comment at top @author Josh Bloch
* @author Neal Gafter
* @version 1.56, 04/21/06
* @see Collection
* @see List
* @see LinkedList
* @see Vector
* @since 1.2

[Campbell Ritchie]

Since the date is given as April 2006, that would appear to be the Java6 version.

[Ganish Patil]

Campbell Ritchie wrote:Since the date is given as April 2006, that would appear to be the Java6 version.

See that's why I really need this forum. Even my senior was baffled why we are not getting correct answer. No one knew we were using older src.zip. Can you please tell me where can I get this source file of Java 8 version from?

Campbell Ritchie wrote:you should leave implementation details well alone.

yes I do understand same way I had left JVM internal architecture but later again my seniors asked me to read it so I read almost thorough artima article which way too old plus little information from JVM specification 8 for method area etc. etc. Anyway at least this new formula made me understand shift operator's working which I abandoned studying.

[Ganish Patil]

Tim Moores wrote:So it would seem that all is as it should be, no?

yes It is using same formula as 7 i.e. int newCapacity = oldCapacity + (oldCapacity >> 1) so all answers in comments are correct. I was looking in older source code.

[Paul Clapham]

Ganish Patil wrote:See that's why I really need this forum.

Although if you asked me to rank this problem on a scale of importance from 1 to 10, I would give it at most a zero.

[Dave Tolls]

Ganish Patil wrote:am I using older src.zip ? Because I got that from my colleague. This is the information found in comment at top @author Josh Bloch

Unless it's changed, but your JDK download should come with a src.zip.

[Ganish Patil]

Dave Tolls wrote:but your JDK download should come with a src.zip.

I have jdk 1.8.0_40 where can I find that src.zip I found javafx-src.zip but not src.zip ?

[Ganish Patil]

@ Paul Clapham Agreed

[Campbell Ritchie]

Ganish Patil wrote:. . . I have jdk 1.8.0_40 where can I find that src.zip I found javafx-src.zip but not src.zip ?

You should be using JDK8u91/92 not 40. Update to 91/92. Look in your Java® installation folder for src.zip. Make sure to check its date before you unzip it.
This is what you will find:-

/*
 * Copyright (c) 1997, 2013, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 * . . .
 */
// . . .

/** * Increases the capacity to ensure that it can hold at least the * number of elements specified by the minimum capacity argument. * * @param minCapacity the desired minimum capacity */ private void grow(int minCapacity) { // overflow-conscious code int oldCapacity = elementData.length; int newCapacity = oldCapacity + (oldCapacity >> 1); if (newCapacity - minCapacity < 0) newCapacity = minCapacity; if (newCapacity - MAX_ARRAY_SIZE > 0) newCapacity = hugeCapacity(minCapacity); // minCapacity is usually close to size, so this is a win: elementData = Arrays.copyOf(elementData, newCapacity); }

[Ganish Patil]

@ Campbell Ritchie Yes installed JDK8u91, also configured src.zip. Thank you so much