John Zukowski has been involved with the Java platform since it was just called Java, since He writes a monthly column for Sun's Core Java Technologies . and their implementation classes in the Collections Framework. Course author: John Zukowski does strategic Java consulting for JZ Ventures, Inc.. His. Java Collections [John Zukowski] on ronaldweinland.info *FREE* shipping on qualifying offers. The Collections Framework is supplied with all versions of the Java 2.
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John Zukowski Chapter 1: Java Collections Framework: An Overview. http ://ronaldweinland.info, respectively. This repository accompanies Java Collections by John Zukowski (Apress, ). Download the files as a zip using the green button, or clone the repository to your machine using Git. Release v corresponds to the code in the published book, without corrections or updates. Java Collections Framework: An Overview. Java Collections Framework: An Overview. John Zukowski. Pages PDF. The Historical Collection Classes.
No part of this work may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or by any information storage or retrieval system, without the prior written permission of the copyright owner and the publisher. ISBN pbk : Trademarked names may appear in this book. Rather than use a trademark symbol with every occurrence of a trademarked name, we use the names only in an editorial fashion and to the benefit of the trademark owner, with no intention of infringement of the trademark. KG, Tiergartenstr. Although every precaution has been taken in the preparation of this work, neither the author nor Apress shall have any liability to any person or entity with respect to any loss or damage caused or alleged to be caused directly or indirectly by the information contained in this work. Acknowledgments Writing this book has been an interesting experience.
Similarly, while the Map and its oft-chosen implementation, HashMap are great for doing name-value or key-value pairs, there's no reason to limit yourself to these familiar tools. You can fix a lot of error prone code with the right API, or even the right Collection. This second article in the 5 things series is the first of several devoted to Collections, because they're so central to what we do in Java programming.
I'll start at the beginning with a look at the quickest but possibly not the most common ways to do everyday things, like swapping out Arrays for Lists. After that we'll delve into lesser known stuff, like writing a custom Collections class and extending the Java Collections API.
Well, we've come a long way since then, and the array's performance advantages generally come up short when weighed against those of the Java Collections libraries. Dumping array contents into a string, for example, requires iterating through the array and concatenating the contents together into a String; whereas, the Collections implementations all have a viable toString implementation.
Except for rare cases, it's good practice to convert any array that comes your way to a collection as quickly as possible.
Which then begs the question, what's the easiest way to make the switch? ArrayToList import java. And, because Arrays. Iterating is inefficient It's not uncommon to want to move the contents of one collection particularly one that was manufactured out of an array over into another collection or to remove a small collection of objects from a larger one.
You might be tempted to simply iterate through the collection and add or remove each element as it's found, but don't.
Iterating, in this case, has major disadvantages: It would be inefficient to resize the collection with each add or remove. There's a potential concurrency nightmare in acquiring a lock, doing the operation, and releasing the lock each time. There's the race condition caused by other threads banging on your collection while the add or remove is taking place.
You can avoid all of these problems by using addAll or removeAll to pass in the collection containing the elements you want to add or remove. For loop through any Iterable The enhanced for loop, one of the great conveniences added to the Java language in Java 5, removed the last barrier to working with Java Collections. Before, developers had to manually obtain an Iterator, use next to obtain the object pointed to from the Iterator, and check to see if more objects were available via hasNext.
Syntactically, [index1][index2]name and [index1]name[index2] are illegal and will result in a compile time error if found in your code. For declarations, it is perfectly legal to place the brackets before type name , after type name , or around type name the variable name.
If you can access the memory in the order it is stored, the access will be most efficient. Normally, this wouldn't matter if everything fit in memory, as computer memory is quick to hop around. However, when using large data structures, linear access performs best and avoids unnecessary swapping. In addition, you can simulate multidimensional arrays by packing them into a one dimensional array. This is done frequently with images. The two manners of packing the one dimensional array are row major order, where the array is filled one row at a time; and column major order, where columns are placed into the array.
Figure 2 5 shows the difference between the two. Figure 2 5: Row major versus column major order. This reads top down, left to right through the image data. When an array is first created, the runtime environment will make sure that the array contents are automatically initialized to some known as opposed to undefined value.
Table 2 1: For instance, the following will create a three element array of names: The array length is set automatically based upon the number of elements in the comma delimited list.
This does not change the length of the array to four, but keeps it at three. This flexibility is primarily for the benefit of code generators. For multidimensional arrays, you would just use an extra set of parenthesis for each added dimension. For instance, the following creates a 6 2 array of years and events. Because the array is declared as an array of Object elements, it is necessary to use the Integer wrapper class to store each int primitive value inside. All elements within an array must be of the array's declared type, or a subclass of that type, in this case, Object, even though all of the elements are subclasses.
Starting with the second dot point Java release Java 1. While it was easy to initialize an array when it was declared, you couldn't reinitialize the array later with a comma delimited list unless you declared another variable to store the new array in.
This is where anonymous arrays step in. With an anonymous array, you can reinitialize an array to a new set of values, or pass unnamed arrays into methods when you don't want to define a local variable to store said array.
Anonymous arrays are declared similarly to regular arrays. However, instead of specifying a length within the square brackets, you place a comma delimited list of values within braces after the brackets, as shown here: Passing Array Arguments and Return Values When an array is passed as an argument to a method, a reference to the array is passed.
This permits you to modify the contents of the array and have the calling routine see the changes to the array when the method returns. In addition, because a reference is passed around, you can also return arrays created within methods and not worry about the garbage collector releasing the array's memory when the method is done.
If you've outgrown the initial size of the array, you need to create a new larger one and copy the original elements into the same location of the larger array. If, however, you don't need to make the array larger, but instead you want to modify the array's elements while keeping the original array intact, you must create a copy or clone of the array.
The arraycopy method of the System class allows you to copy elements from one array to another. When making this copy, the destination array can be larger; but if the destination is smaller, an ArrayIndexOutOfBoundsException will be thrown at runtime. The arraycopy method takes five arguments two for each array and starting position, and one for the number of elements to copy: Besides type compatibility, the only requirement here is that the destination array's memory is already allocated.
Warning When copying elements between different arrays, if the source or destination arguments are not arrays or their types are not compatible, an ArrayStoreException will be thrown.
Incompatible arrays would be where one is an array of primitives and the other is an array of objects; or the primitive types are different; or the object types are not assignable. To demonstrate, Listing 2 2 takes an integer array and creates a new array that is twice as large. The doublearray method in the following example does this for us: Listing 2 2: Doubling the size of an array. After you learn about array reflection in a later section, you can generalize the method to double the size of an array of any type.
When executed, the program generates the following output: Original size: This works even if there is some overlap. Since arrays implement the Cloneable interface, besides copying regions of arrays, you can also clone them. Cloning involves creating a new array of the same size and type and copying all the old elements into the new array. This is unlike copying, which requires you to create and size the destination array yourself.
In the case of primitive elements, the new array has copies of the old elements, so changes to the elements of one are not reflected in the copy. However, in the case of object references, only the reference is copied. Thus, both copies of the array would point to the same object. Changes to that object would be reflected in both arrays. This is called a shallow copy or shallow clone. To demonstrate, the following method takes one integer array and returns a copy of said array. Array Immutability It is useful to return an array clone from a method if you don't want the caller of your method to modify the underlying array structure.
While you can declare arrays to be final, as in the following example: It only limits you from changing what the final variable refers to. While the following line results in a compilation error: Either interface provides access to the individual elements without exposing the whole array to changes or requiring you to make a copy of the entire array.
You'll learn more about these interfaces in later chapters. Array Assignments Array assignments work like variable assignments. If variable x is a reference to an array of y, then x can be a reference to z if a variable of type z can be assigned to y.
Because a Button variable can be assigned to a Component variable, a Changing an array element for one array changes the element for both.
Figure 2 6: Shared memory after an array assignment. If, after assigning an array variable to a superclass array variable as in the prior example of assigning the button array to a component array variable you then try to place a different subclass instance into the array, an ArrayStoreException is thrown.
To continue the prior example, an ArrayStoreException would be thrown if you tried to place a Canvas into the components array.
Even though the components array is declared as an array of Component objects, because the components array specifically refers to an array of Button objects, Canvas objects cannot be stored in the array. This is a run time exception as the actual assignment is legal from the perspective of a type safe compiler. Checking for Array Equality Checking for equality between two arrays can be done in one of two manners depending upon the type of equality you are looking for.
Are the array variables pointing to the same place in memory and thus pointing to the same array? Or are the elements of two arrays comparatively equivalent? For example, the prior components and buttons variables would be equal in this case since one is a reference to the other: Since these arrays have the same elements but exist in different memory space, they are different.
In order to have a clone of an array be "equal" to the original, you must use the equals method of the java. In the case where the arguments are arrays of objects, the equals method of each object will be used to check for equality.
For more information on the Arrays class, see Chapter Array Reflection If for some reason you are ever unsure whether an argument or object is an array, you can retrieve the object's Class object and ask it. The isarray method of the Class class will tell you.
Once you know you have an array, you can ask the getcomponenttype method of Class what type of array you actually have. The getcomponenttype method returns null if the isarray method returns false.
Otherwise, the Class type of the element is returned. You can recursively call isarray if the array is multidimensional. It will still have only one component type. In addition, you can use the getlength method of the Array class found in the java.
To demonstrate, Listing 2 3 shows that the argument to the main method is an array of java.
Listing 2 3: Using reflection to check array type and length. If you don't use the isarray and getcomponenttype methods and you try to print the Class type for an array, you'll get a string that includes a [ followed by a letter and the class name or no class name if a primitive.
For instance, if you tried to print out the type variable in the printtype method above, you would get class [Ljava. String; as the output. In addition to asking an object if it is an array and what type of array it is, you can also create arrays at runtime with the java. This might be helpful to create generic utility routines that perform array tasks such as size doubling.
We'll return to that shortly. To create a new array, use the newinstance method of Array, which comes in two varieties. For single dimension arrays you would normally use the simpler version, which acts like the statement new type[length] and returns the array as an object: For instance, the following creates an array with room for five integers: Concrete collections in Java library Java Collection framework: On concrete collections and their implementation 1 ArrayList: What is the most important feature of Java?
Java is a platform independent language. What do you mean by platform independence? Platform independence means that we can write and compile the java. Vectors can resize themselves dynamically. Inserting elements into a Vector whose current size is less than its capacity is a relatively. Introduction to Computation and Problem Solving Class The Java Collections Framework Prof.
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An Introduction to the Java Programming Language History of Java In , a group of Sun Microsystems engineers led by James Gosling decided to develop a language for consumer devices cable boxes, etc. It is primarily an imperative language but support for functional. The memory address of the first element of an array is called A. The memory address of fifth element of an array can be calculated. Chapter 8: Bags and Sets In the stack and the queue abstractions, the order that elements are placed into the container is important, because the order elements are removed is related to the order in which.
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Printed in U. First printing. About the authors John Zukowski has been involved with the Java platform since it was just called Java, since Show all. From the reviews: Table of contents 19 chapters Table of contents 19 chapters Java Collections Framework: An Overview Zukowski, John Pages Arrays Zukowski, John Pages Collections Introduction Zukowski, John Pages Sets Zukowski, John Pages Lists Zukowski, John Pages