Introduction to java programming
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This document introduces Java as a popular, object-oriented programming language that is platform-independent and secure, making it suitable for web programming. It covers key concepts such as applets, servlets, the Java Virtual Machine, and the fundamentals of Java syntax, including primitive data types, expressions, control statements, and class definitions. Additionally, it provides examples of declaring variables, creating classes, and using objects.
![HelloWorld
• Note that String is built in
• println is a member function for the System.out class
public class HelloWorld {
public static void main(String[] args) {
System.out.println("Hello World!");
}
}](https://image.slidesharecdn.com/introductiontojavaprogramming-150518051143-lva1-app6891/85/Introduction-to-java-programming-5-320.jpg)
![An array is an object
• Person mary = new Person ( );
• int myArray[ ] = new int[5];
• or:
• int myArray[ ] = {1, 4, 9, 16, 25};
• String languages [ ] = {"Prolog", "Java"};](https://image.slidesharecdn.com/introductiontojavaprogramming-150518051143-lva1-app6891/85/Introduction-to-java-programming-14-320.jpg)
Introduction to java programming
- 2. Why Java? •It’s the current “hot” language •It’s almost entirely object-oriented •It has a vast library of predefined objects and operations •It’s more platform independent • this makes it great for Web programming •It’s more secure •It isn’t C++
- 3. Applets, Servlets and Applications •An applet is designed to be embedded in a Web page, and run by a browser •Applets run in a sandbox with numerous restrictions; for example, they can’t read files and then use the network •A servlet is designed to be run by a web server •An application is a conventional program
- 4. Java Virtual Machine •The .class files generated by the compiler are not executable binaries • so Java combines compilation and interpretation •Instead, they contain “byte-codes” to be executed by the Java Virtual Machine • other languages have done this, e.g. UCSD Pascal •This approach provides platform independence, and greater security
- 5. HelloWorld • Note that String is built in • println is a member function for the System.out class public class HelloWorld { public static void main(String[] args) { System.out.println("Hello World!"); } }
- 6. Comments are almost like C++ • /* This kind of comment can span multiple lines */ • // This kind is to the end of the line • /** * This kind of comment is a special * ‘javadoc’ style comment */
- 7. Primitive data types are like C Main data types are int, double, boolean, char Also have byte, short, long, float boolean has values true and false Declarations look like C, for example, double x, y; int count = 0;
- 8. Expressions are like C •Assignment statements mostly look like those in C; you can use =, +=, *= etc. •Arithmetic uses the familiar + - * / % •Java also has ++ and -- •Java has boolean operators && || ! •Java has comparisons < <= == != >= > •Java does not have pointers or pointer arithmetic
- 9. Control statements are like C if (x < y) smaller = x; if (x < y){ smaller=x;sum += x;} else { smaller = y; sum += y; } while (x < y) { y = y - x; } do { y = y - x; } while (x < y) for (int i = 0; i < max; i++) sum += i;
- 10. what is a class? •A class consists of • a collection of fields, or variables, very much like the named fields of a struct • all the operations (called methods) that can be performed on those fields • can be instantiated •A class describes objects and operations defined on those objects
- 11. Name conventions • Java is case-sensitive; maxval, maxVal, and MaxVal are three different names • Class names begin with a capital letter • All other names begin with a lowercase letter • Subsequent words are capitalized: theBigOne • Underscores are not used in names • These are very strong conventions!
- 12. An example of a class class Person { String name; int age; void birthday ( ) { age++; System.out.println (name + ' is now ' + age); } }
- 13. Creating and using an object •Person john; john = new Person ( ); john.name = "John Smith"; john.age = 37; •Person mary = new Person ( ); mary.name = "Mary Brown"; mary.age = 33; mary.birthday ( );
- 14. An array is an object • Person mary = new Person ( ); • int myArray[ ] = new int[5]; • or: • int myArray[ ] = {1, 4, 9, 16, 25}; • String languages [ ] = {"Prolog", "Java"};