201871010111- Liu Jiahua "object-oriented programming (java)" the second week of learning summary
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Part I: similarities and differences between Java and C combined with relatively basic grammar, summarizes theoretical knowledge this week
3.1 Basics
Identifier:
A, identified by letters, underline, dollar signs and numbers, and the first symbol is not a number.
B, these are all valid identifiers:
Hello, $ 1234, the program name, www_123
C, an identifier may be used: a class name, variable name, a method name, array name, file name, etc.
Key words:
A, is the java language specific word has been given a specific meaning
B, common are: class, public, try, catch, if, float, import, void and so on.
C, variable names do keyword
Comment:
Java annotations in three ways:
1. //
Notes // contents have been made to this end of the line.
2. / * and * /
define a comment block.
3. / ** start, * / end
this annotation method can be used to automatically generate documentation.
3.2 Data Types
There are eight basic types of Java
- integer types (int, short, long, byte ) - floating-point type (float, double)
- character type (char) - boolean (boolean)
3.3 Variable
* In Java, every variable belonging to one type. When you declare a variable, the variable type belongs to precede the variable name.
– double salary； – int vacationDays;
– long earthPopulation; – boolean done;
* In Java, a line can declare multiple variables. Individually declare each variable can improve the readability of the program.
– int i,j；//both are integers
Variable initialization
* After a variable declaration must be explicitly initialized by assignment to it - Never use an uninitialized variable's value.
* In Java, you can declare a variable anywhere in the code. Declare variables should be as close as possible to the local variable is first used, easy to read and use.
* In Java, you can not declare a variable within the same scope of two of the same name.
Defining constants
* In Java, use the keyword final to indicate constants. Traditionally constant names are capitalized.
final double CM_PER_INCH=2.54；
* Keyword final representation can only assign a value to a variable, its value once set, can not follow the code and then modify it.
* In Java, often want a constant can be used in multiple methods in a class, these constants are usually called class constants. You can use the keyword static final declare a class constants (class constants).
public static final double CM_PER_INCH
3.4 Operators
* Various operators: and related object-oriented computing
- new - it is used to create an object operator.
- Instanceof - returns a Boolean value that indicates whether an object is an instance of a particular class or its subclasses.
* Operator precedence and associativity
* Mathematical functions and constants
- Mathematical functions included in the Math class.
- power function, trigonometric, exponential, and other inverse function and so on.
- Java also provides two constants.
-Math.PI
-Math.E
- If we are not in front of a mathematical method name and constant name prefix ". Math", you can add the following code at the top of the source file: -impot static java.lang.Math *;.
3.5 Type Conversion
3.6 String
* Java string is a sequence of Unicode characters, which is the basic character of the data structure of the organization, similar to the use of an array of characters.
* A built-in string type, but provides a Java String predefined classes in the standard Java class library. In Java, strings are treated as objects to deal with.
* Strings need to use the program can be divided into two categories:
- After you create will not do modifications and variations of immutable string String class;
- It does allow modifications and variations to build a string StringBuilder class after creation.
3.7 Input Output
* Read input
* Formatted output
* File Input and Output
3.8 Control Process
3.9 Large value
* If the basic integer and floating point data type can not achieve the required accuracy, then the package may be used java.math two classes, a BigInteger and BigDecimal. These two classes may operate any longer intended number.
* BigInteger class implements arbitrary-precision integer arithmetic, B igDecimal achieve arbitrary-precision floating-point arithmetic.
3.10 Array
* Array is a data structure that is an ordered set of data, the data type of each element of the array is the same.
* Identify the elements is achieved by the array name and an index to it, and
As a [0] a first element of the array represents, a [. 1] array representing
the second element a, and so on.
Part II: Experimental part
Experiment name: Experiment two basic Java programming (1)
1. Purpose:
(1) become more familiar with the basic steps of the java program development and IDE command line in two ways;
（2）掌握Eclipse集成开发环境下导入Java源程序的过程；
（3）掌握Java语言构造基本程序的数据类型、变量、运算符、各类表达式、输入输出、流程控制的基本语法；
（4）掌握Math类、String类、StringBuilder类的用法。
2. 实验步骤与内容：
实验1 程序互评
评分要求：结合评分程序的运行情况，给出评分程序成绩，满分5分，每个错误扣1分，扣至0分为止；
评分者每发现一个正确的错误，本人实验1得分加1分，最高加5分。
实验2：编写包含以下代码片段的java应用程序，输出字符串类对象s3的值。
| String s1=“Hello!”; String s2=“World”; String s3=s1+s2; |
代码如下：
package MyProject; public class Week2SX2 { public static void main(String[] args)
{ // TODO Auto-generated method stub String s1 ="Hello!"; String s2= "World"; String s3=s1+s2; System.out.println(s3); } }
运行结果如下：
实验3：更改实验2中s1、s2、s3为StringBuilder类对象，观察程序运行结果并与实验2结果进行对比，理解String类对象与StringBuilder类对象的区别。
代码如下：
package MyProject; public class Week2SX3 { public static void main(String[] args)
{ StringBuilder s1=new StringBuilder("Hello!"); StringBuilder s2=new StringBuilder("world"); StringBuilder s3=new StringBuilder(); s3.append(s1); //append 字符拼接 s3.append(s2); System.out.println(s3); } }
运行结果如下：
实验4：在命令行方式下调试运行下列程序，理解java应用程序命令行参数的用法。
package MyProject; public class Message { public static void main(String[] args) { if (args[0].equals("-h")) System.out.print("Hello"); else if(args[0].equals("-g")) System.out.print("goodbye,"); for(int i=1;i<args.length;i++) System.out.print(" "+args[i]); System.out.println("!"); } }
运行截图如下：
实验5：Eclipse环境下导入第3章示例程序InputTest.java步骤：
(1） 新建java project如下图：
（2） 选择File->import->File ystem->Next，打开文件导入窗口如下图，点击上方Browse选择导入源程序并选中，点击下方Browse选择源程序导入位置为新项目InputTest/src位置后，点击finish完成导入。
（3） 打开InputTest项目src文件夹的缺省包，双击InputTest.java在IDE源程序编辑区打开文件。
（4） 右键单击InputTest.java文件名打开快捷菜单，选择Run as->java application运行此程序，结合程序运行结果，理解代码中Scanner类对象用法，掌握java控制台输入方法。
实验6：按照实验5操作步骤，导入WriteReadFileTest.java示例程序，运行程序并理解程序代码,观察项目文件夹下文件myfile.txt的内容，掌握文件的输入输出操作。
实验7：按照实验5的操作步骤，导入第3章3-3——3-4示例程序，掌握两个程序循环控制结构的用途。
3-3示例程序运行结果：
3-4示例程序运行结果：
实验8：按照实验5的操作步骤，导入第3章3-5示例程序，理解抽奖概率计算算法。
第三部分：实验总结
通过上周对基础理论的学习以及对eclipse运用的初步掌握，在此次实验过程中，在程序的书写和格式上出错率比上次明显少了很多。此次实验
进一步熟悉命令行和IDE两种方式下java程序开发的基本步骤，学习了如何向eclipse导入其他文件夹中的程序，掌握Java语言构造基本程序的数据类型、变量、
运算符、各类表达式、输入输出、流程控制的基本语法。
在实验过程中，逐渐了解并熟悉了String类和StringBulider类的一些基本方法。通过本次学习，我发现了在Java中认识标识符很重要，另外，我掌握了更多的语法，虽然都还只是基础，但我会继续努力学习，在以后的学习中不断提高自己的编程水平。