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Unit2: Object-oriented programming Getting started with Java

Unit2: Object-oriented programming Getting started with Java. Jin Sa. Objectives of this unit. To understand relevant terminologies To know the basic syntax of a Java program and methods To be able to write, compile and run simple Java programs To know how to group classes into packages

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Unit2: Object-oriented programming Getting started with Java

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  1. Unit2: Object-oriented programmingGetting started with Java Jin Sa

  2. Objectives of this unit • To understand relevant terminologies • To know the basic syntax of a Java program and methods • To be able to write, compile and run simple Java programs • To know how to group classes into packages • To know how to use the Scanner class • To know how to create, compile and run Java programs using NetBeans

  3. Terminologies • Java 2 Platform, Standard Edition (J2SE) • Java 2 Platform, Enterprise Edition (J2EE) • Java Development Toolkit (JDK), set of tools such as compiler (javac), documentation generator (javadoc) and debugger • Java API: predefined classes and interfaces for developing java programs. • Integrated development environment (IDE): integrate tools such as compiler and debugger to provide facilities for programmers to develop software, e.g. NetBeans incorporates the development tools of the JDK into one convenient GUI-based program.

  4. A Simple Java program //This program prints Welcome to Java! public class Welcome { public static void main(String[] args){ System.out.println(“Welcome to Java!"); } }

  5. Develop and run the Java program without IDE • Name of the file must be the same as the name of the class with .java, • e.g. Welcome.java • Convention: class name starts with capital letter • To compile • javac Welcome.java • Generates a class file called Welcome.class • To run • java Welcome

  6. Develop and run Java programs using IDE (NetBeans) • incorporates the Java compiler, the Java interpreter and other tools together with file and project management for developing and executing Java programs. • Student activity 2.1. in section C.3. Following NetBeans tutorial on how to create and run a java program using NetBeans • Student activity 2.2 in section C.3, create the Welcome program using NetBeans

  7. Some basic language features • Referenece: Sun’s tutorial on Java (Language basics http://java.sun.com/docs/books/tutorial/java/nutsandbolts/index.html • Package • Scanner • Loop • Switch • Array • Method

  8. Package and import • Everything in java is part of a class. • Packages are used to group classes • Package can contain other packages • Java expects a one-to-one mapping of the package name and the file system directory structure • Every class in Java belongs to a package, to put a class in a package, include this line as the first line • package packagename; • If not, the class is in a default unnamed package

  9. Welcome class in the startjava package package startjava; //This program prints Welcome to Java! public class Welcome { public static void main(String[] args) { System.out.println(“Welcome to Java!"); } }

  10. Use classes from other packages • Use the fully qualified name of the class. E.g. the fully qualified name for the Scanner class is • java.util.Scanner. • Or use the “import” statement. For example, to import the Scanner class from the java.util package, you use • import java.util.Scanner; You can also import all the classes in a package, e.g. • import java.util.*; The import statement tells the compiler where to locate the classes.

  11. Input using Scanner package startjava; import java.util.Scanner; //This program prints Welcome to Java!+the name public class Welcome { public static void main(String[] args) { String name=""; Scanner scan = new Scanner(System.in); System.out.println("Enter your name:"); name=scan.nextLine(); System.out.println("Welcome to Java! "+name); } }

  12. Loop and switch in Java • Read unit 2 “Example 1: Calculating total – using loop” in section D.3 • Complete Student Activity 2.3 • Read unit 2 Example 2: Option menu – using switch in section D.4 • Complete Student Activity 2.4

  13. Array in Java • Read unit 2 “Example 3: An Example with an array” in section D.5 • Complete Student Activity 2.5

  14. An example of using methods public class Welcome1 { public static void main(String[] args) { prompt(); String name=getName(); System.out.println(name); } public static void prompt(){ System.out.println(“Enter your name”); } public static String getName(){ Scanner in=new Scanner(System.in); String nm=in.nextLine(); return nm; } }

  15. Using methods • Read unit 2 “Example 4: An example with a method” in section D.6 • Complete Student Activity 2.6

  16. Summary In this unit, we have • introduced some well known terminology related to programming in Java • explained how to use NetBeans • demonstrated how to write simple Java programs using NetBeans • introduced the concept of package • illustrated how to use the Scanner class for input • covered some basic program concepts including array, loop, conditional statement and methods.

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