OCA Java SE 8程序员认证指南学习摘要：从基础到实战

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本资源是《OCA Oracle Certified Associate Java SE 8 Programmer I Study Guide》的样本章节，由Mala Gupta撰写，专为准备Oracle Certified Associate Java SE 8 Programmer I (1Z0-809)认证考试的学习者提供指导。章节1概述了Java基础，是理解后续章节的关键。 1. **Java基础** - 学习者需要掌握Java类的基本结构，包括：package（包）和import语句，用于组织和引入其他类；class声明，定义类的行为和属性；注释，提供代码解释；变量，存储数据；以及方法，实现功能。理解这些组件之间的关系对于编写有效的Java代码至关重要。 2. **执行Java应用程序与main方法** - 考察的重点是创建可执行的Java应用程序，需要知道如何在程序中添加一个main方法，这是程序的入口点。正确的方法签名（如`public static void main(String[] args)`）对于使程序成为可执行文件至关重要。此外，还需要了解如何在命令行中运行Java程序，并处理控制台输出。 3. **导入包** 学习者需要理解如何导入其他Java包，以便在自己的代码中使用它们提供的类和接口。包是Java语言的一个核心特性，它帮助组织和避免命名冲突，使得代码更易维护。 4. **工作原理与实践** 章节内容还包括对Java数据类型的操作，方法和封装的概念，以及使用Java API中的特定类和数组。这些都是Java编程的基础，对实现各种功能至关重要。 5. **流程控制** 学习者会学习到如何通过条件语句（如if-else、switch）、循环（for, while）等进行程序流程的控制，这是程序逻辑的重要组成部分。 6. **继承和多态** 遵循面向对象编程原则，章节将讲解继承的概念，如何创建子类继承父类的属性和方法，以及多态如何允许使用统一接口处理不同类型的对象。 7. **异常处理** 异常处理是任何高质量代码不可或缺的一部分，本章节涵盖如何捕获、处理和抛出异常，确保程序在遇到错误时能优雅地处理。 8. **模拟全真考试** 最后，章节末尾提供了全模拟考试，帮助考生熟悉考试格式和实际考试中可能遇到的问题，进行实战演练和评估。通过这个章节，学习者将建立起坚实的Java基础，为深入学习和备考Oracle OCA Java SE 8 Programmer I认证打下坚实的基础。

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31The structures of a Java class and a source code file

LASS

DEFINITION

A class is a design used to specify the attributes and behavior of an object. The attri-

butes of an object are implemented using variables, and the behavior is implemented

using methods. For example, consider a class as being like the design or specification of

a mobile phone, and a mobile phone as being an object of that design. The same

design can be used to create multiple mobile phones, just as the Java Virtual Machine

(JVM) uses a class to create its objects. You can also consider a class as being like a

mold that you can use to create meaningful and useful objects. A class is a design from

which an object can be created.

Let’s define a simple class to represent a mobile phone:

class Phone {

String model;

String company;

Phone(String model) {

this.model = model;

}

double weight;

void makeCall(String number) {

// code

}

void receiveCall() {

// code

}

Points to remember:

■

A class name starts with the keyword

class

. Watch out for the case of the key-

word

class

. Java is cAsE-sEnSiTivE.

class

(lowercase c) isn’t the same as

Class

(uppercase C). You can’t use the word

Class

(uppercase C) to define a class.

■

The state of a class is defined using attributes or instance variables.

■

It isn’t compulsory to define all attributes of a class before defining its methods

(the variable

weight

is defined after

Phone

’s constructor). But this is far from

being optimal for readability.

■

The behavior is defined using methods, which may include method parameters.

■

A class definition may also include comments and constructors.

NOTE

A class is a design from which an object can be created.

ARIABLES

Revisit the definition of the class

Phone

in the previous example. Because the variables

model

company

, and

weight

are used to store the state of an object (also called an

instance), they’re called instance variables or instance attributes. Each object has its own

copy of the instance variables. If you change the value of an instance variable for an

object, the value for the same named instance variable won’t change for another object.

The instance variables are defined within a class but outside all methods in a class.

32 C

HAPTER

1 Java basics

A single copy of a class variable or

static

variable is shared by all the objects of a

class. The

static

variables are covered in section 1.5.3 with a detailed discussion of

the nonaccess modifier

static

ETHODS

Again, revisit the previous example. The methods

makeCall

and

receiveCall

are

instance methods, which are generally used to manipulate the instance variables.

A class method or static method can be used to manipulate the

static

variables, as dis-

cussed in detail in section 1.5.3.

ONSTRUCTORS

Class

Phone

in the previous example defines a single constructor. A class constructor is

used to create and initialize the objects of a class. A class can define multiple construc-

tors that accept different sets of method parameters.

1.1.2 Structure and components of a Java source code file

A Java source code file is used to define Java entities such as a class, interface, enum,

and annotation.

NOTE

Java annotations are not on the exam and so won’t be discussed in

this book.

All your Java code should be defined in Java source code files (text files whose names

end with .java). The exam covers the following aspects of the structure of a Java source

code file:

■

Definition of a class and an interface in a Java source code file

■

Definition of single or multiple classes and interfaces within the same Java

source code file

■

Application of

import

and

package

statements to all the classes in a Java source

code file

We’ve already covered the detailed structure and definition of classes in section 1.1.1.

Let’s get started with the definition of an interface.

EFINITION

INTERFACE

AVA

SOURCE

CODE

FILE

An interface specifies a contract for the classes to implement. You can compare imple-

menting an interface to signing a contract. An interface is a grouping of related meth-

ods and constants. Prior to Java 8, interface methods were implicitly abstract. But

starting with Java version 8, the methods in an interface can define a default imple-

mentation. With Java 8, interfaces can also define

static

methods.

Here’s a quick example to help you understand the essence of interfaces. No mat-

ter which brand of television each of us has, every television provides the common

functionality of changing the channel and adjusting the volume. You can compare the

controls of a television set to an interface and the design of a television set to a class

that implements the interface controls.

33The structures of a Java class and a source code file

Let’s define this interface:

interface Controls {

void changeChannel(int channelNumber);

void increaseVolume();

void decreaseVolume();

}

The definition of an interface starts with the keyword

interface

. Remember, Java is

case-sensitive, so you can’t use the word

Interface

(with a capital I) to define an inter-

face. This section provides a brief overview of interfaces. You’ll work with interfaces in

detail in chapter 6.

EFINITION

SINGLE

AND

MULTIPLE

CLASSES

SINGLE

AVA

SOURCE

CODE

FILE

You can define either a single class or an interface in a Java source code file or multi-

ple such entities. Let’s start with a simple example: a Java source code file called

SingleClass.java that defines a single class

SingleClass

class SingleClass {