java面向对象编程1.1.1-1.1.3

To declare two variables of type GregorianCalendar, we would type:
java.util.GregorianCalendar firstDate = new java.util.GregorianCalendar(2004, 1, 1); java.util.GregorianCalendar lastDate = new java.util.GregorianCalendar(2004, 12, 31);
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It is not necessary to import ng. The ng package is implicitly imported into all Java applications. All applications can reference classes in the ng package using their simple names.
面向对象程序设计导论(SSD3)
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1: Introduction to Information Systems
2: Introduction to Computer Systems
4 : User Centered Design and Testing
3: Object Oriented Programming and Design
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The command java calls the Java interpreter and MyApplication is the name of the class that will be executed.
The operating system begins execution by calling the method main in the class MyApplication.
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Applications can consist of one or many classes; one of those classes must have a method main.
The method main has the following signature. public static void main(String[] args)
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Packages and the import Statement The classes in the Java API are grouped into packages. A package is simply a collection of related classes. An example of a package name: java.util The fully qualified name of a class that is part of a package is the package name and the class name separated by a dot. java.util.GregorianCalendar
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public class MyApplication { public static void main(String[ ] args) { System.out.println("This is my first aplication!"); } }
Listing 2 MyApplication.java
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java.util.GregorianCalendar
java.util.GregorianCalendar firstDate = new java.util.GregorianCalendar(2004, 1, 1);
int float
i = 5; y = 7.2;
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Java offers the import statement. It is used to "import" a class—or an entire package of classes—into a file. An import statement consists of the keyword import, a fully qualified name, and a semicolon: import java.util.GregorianCalendar; This statement, placed at the top of a file, makes it possible to write:
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The ng.String Class Java provides no primitive string type. Java does include the string literal, a sequence of characters within double quotes such as "abc". A string literal is an instance of class String.
Applets are referenced from web pages and interpreted by web browsers. Every applet contains a public class that extends the class Applet.
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import java.applet.*; import java.awt.*; public class MyApplet extends Applet { public void paint(Graphics g) { g.drawString("This is an applet!\n", 10, 10); } }
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Applications in Java
"stand-alone" programs, interpreted by a Java interpreter (not a web browser) on a host system.
Figure 1 Command to execute MyApplication
Listing 2 MyApplication.java
The file containing the source code must have the same name as the class it contains and use the .java extension. For example, the file containing the class WordCount must be named WordCount.java.
Class names should have the first character of each word capitalized and they should not contain any underscores ( _ ).
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public class MyApplication { public static void main(String[ ] args) { System.out.println("This is my first aplication!"); } }
8: Networks and Distributed Computing
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参考书
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总成绩＝平时成绩＋期末考试 平时成绩: 每次课的作业＋课堂抽查
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平时作业
Exercise 1~8 Quiz


Multiple-Choice
/~hejun
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作业提交
7: Database Systems
5: Data Structures and Algorithms
6: System Level Programming
9: Software Specification, Test and Maintenance
10: Software Project Organization and Managemion of MyApplication
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1.1.3 Beginning with the Java API Introduction
The Java Application Programming Interface (API) represents an extensive Java library. The documentation for the Java API is generated by the Javadoc tool.
•String(). Constructs a new String object that represents an empty character sequence. •String(char[] value). Constructs a new String object that represents the sequence of characters contained in the character array. •String(String original). Constructs a new String object that represents the same sequence of characters as the argument. •int size(). Obtains the number of characters in the String. •char charAt(int index). Returns the character at the specified index. •boolean equals(Object anObject). Returns true if the specified Object represents a String with the same sequence of characters. •int indexOf(int ch). Returns the index of the first occurrence of the character. •int indexOf(String str). Returns the index of the first occurrence of the String. •boolean startsWith(String prefix). Checks if the String has the specified prefix. •String substring(int beginIndex, int endIndex). Returns a substring. 22