Java核心技术职业生涯指南

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"Core Java Career Essentials" 本书《Core Java Career Essentials》是针对Java开发人员的一份重要参考资料，由Arulkumaran Kumaraswamipillai和Sivayini Arulkumaran共同撰写，旨在帮助读者深入理解Java平台、语言、类、对象、面向对象的概念与原则、数据结构、算法以及模式匹配的基础知识。本书适用于那些希望在Java领域建立职业发展的人士。书中的内容涵盖了以下几个关键领域： 1. **Java平台**：包括Java虚拟机（JVM）、Java标准版（Java SE）和企业版（Java EE）的基本概念，以及Java运行环境的配置和管理。 2. **Java语言**：深入讲解Java语法、控制流、异常处理、封装、继承和多态等核心特性，帮助读者掌握编写高效、健壮的Java代码。 3. **类和对象**：探讨如何设计和实现类，以及如何通过对象进行编程，强调面向对象设计的基本原则和最佳实践。 4. **面向对象概念与原则**：介绍封装、继承和多态三大面向对象特性，以及设计模式的应用，使读者能够理解和应用这些基本的软件设计原则。 5. **数据结构**：涵盖常见的数据结构如数组、链表、栈、队列、树和图，以及它们在实际问题中的应用，帮助读者理解如何有效地存储和处理数据。 6. **算法**：讲解排序、搜索、图算法等基础算法，提升解决问题的能力和程序的效率。 7. **模式匹配**：讨论正则表达式和模式匹配在文本处理和数据验证中的作用，帮助开发者提高代码的可读性和灵活性。书中特别指出，尽管作者已经尽力确保信息的准确性，但不提供任何形式的保证，无论是明示的还是默示的。如果读者发现任何技术性、语法或拼写错误，可以通过邮件向java-interview@hotmail.com提供反馈和修正建议。此外，更多关于Java和Java企业级开发的职业资源可以在http://www.lulu.com/java-success找到。感谢审阅者Ankit Garg、Devaka Cooray、Roberto Perillo、Rod Good和Sean Clynes的贡献，他们的专业意见确保了本书的质量。《Core Java Career Essentials》是一本全面的Java学习指南，它不仅涵盖了基础理论，还强调了实践应用，对于希望在Java开发领域深化技能和提升职业生涯的人来说，是一本理想的伴侣书籍。

Platform Essentials

Why use Java?

Give a few reasons for using Java? LF PF FAQ OEQ

A1 One needs to use the best tool for the job, whether that tool is Java or not. When

choosing a technology to solve your business problems, you need to consider many

factors like development cost, infrastructure cost, ongoing support cost, robustness,

flexibility, security, performance, etc.

Java provides client technologies, server technologies, and integration technologies to

solve small scale to very large scale business problems.

• If you want to target multiple platforms, Java is the best solution. Although the

notion of “Write Once Run Anywhere (WORA)” does not always hold true,

but it is true that the majority of the code you write in Java will run almost

anywhere.

• The emergence of open-source technologies has truly made Java a powerful

competitor in the server and integration technology space. You can always find

a proven framework that best solves your business problems. For example,

http://java-source.net/, http://projects.apache.org/indexes/category.html

http://www.springsource.org/

• The Java platform has been around for a while and has been tested and

deployed in many industries. It is mature both in terms of implementation as

well as APIs. There's less risk that there's some bug in the platform that poses

security risks, or has some intrinsic flaw in its architecture.

• The Java platform is standardized and the specifications are publicly available

from various sources. There are many books, on-line resources, tutorials, and

training courses on how to develop on it. Hence, it'll be easier to find

developers who can be productive sooner.

• There are plethora of design, development, and deployment tools both open-

source and commercial to choose from.

• The platform also comes with a rich set of APIs. This means developers spend

Platform Essentials

• Java does not support destructors, but adds a finalize( ) method. Finalize

methods are invoked by the garbage collector prior to reclaiming the memory

occupied by the object, which has the finalize( ) method. This means, you do

not know when the objects are going to be finalized. Avoid using finalize( )

method to release non-memory resources like file handles, sockets, database

connections, etc because the platform has only a finite number of these

resources, and you do not know when the garbage collection is going to

kick in to release these resources through the finalize( ) method.

• Java does not include structures or unions because the traditional data struc@

tures are implemented as an object oriented Java Collections framework.

• All the code in Java program is encapsulated within classes therefore Java does

not have global variables or functions.

• C++ requires explicit memory management while Java includes automatic

garbage collection.

• Generics in Java provides a simple compile-time type safety check whereas in

C++ whenever a template class is instantiated with a new class, the entire code

for that class is reproduced and recompiled for the new class.

Is Java 100% object oriented? If yes, why? And if not, why not? LF FAQ OEQ

A3 I would say Java is not 100% object oriented, but it embodies practical OO concepts.

There are 6 qualities to make a programming language to be pure object oriented. They

are:

1. Encapsulation – data hiding and modularity.

2. Inheritance. – you define new classes and behavior based on existing classes to

obtain code reuse.

3. Polymorphism – the same message sent to different objects results in behavior

that's dependent on the nature of the object receiving the message.

4. All predefined types are objects.

5. All operations are performed by sending messages to objects.

6. All user defined types are objects.

The main reason why Java cannot be considered 100% OO is due to its existence of 8

primitive variables (i.e. violates point number 4) like int, long, char, float, etc. These

data types have been excused from being objects for simplicity and to improve

performance. Since primitive data types are not objects, they don't have any qualities

such as inheritance or polymorphism. Even though Java provides immutable wrapper

classes like Integer, Long, Character, etc representing corresponding primitive data as

objects, the fact that it allowed non object oriented primitive variables to exist, makes it

not fully OO.

Another reason why Java is considered not full OO is due to its existence of static

methods and variables (i.e. violates point number 5). Since static methods can be

invoked without instantiating an object, we could say that it breaks the rules of encap@

sulation.

Java does not support multiple class inheritance because different classes may have

different variables with same name that may be contradicted and can cause confusions

and result in errors. We could also argue that Java is not 100% OO according to this

point of view. But Java realizes some of the key benefits of multiple inheritance

through its support for multiple interface inheritance. The multiple interface inher@

itance gives simplicity by avoiding ambiguity, complexity, misuse, and potential

increased memory usage that is present in multiple class inheritance.

Operator overloading is not possible in Java except for string concatenation and

addition operations. String concatenation and addition example,

System.out.println(1 + 2 + ”3”); //outputs 33

System.out.println(“1” + 2 + 3); //outputs 123

Since this is a kind of polymorphism for other operators like * (multiplication), /

(division), or - (subtraction), and Java does not support this, hence one could debate

that Java is not 100% OO. Working with a primitive in Java is more elegant than

working with an object like BigDecimal. For example,

int a,b, c;

//without operator overloading

a = b – c * d

What happens in Java when you have to deal with large decimal numbers that must be

accurate and of unlimited size and precision? You must use a BigDecimal. BigDecimal

Platform Essentials

looks verbose for larger calculations without the operator overloading as shown below:

BigDecimal b = new BigDecimal(“25.24”);

BigDecimal c = new BigDecimal(“3.99”);

BigDecimal d = new BigDecimal(“2.78”);

BigDecimal a = b.subtract(c.multiply(d)); //verbose

Java 7 may have operator overloading for BigDecimal, and it would make your code

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