The 1 st tutoring session of CSc2310 Fall, 2012

1. The 1st tutoring session of CSc2310Fall, 2012 HaidongXue

2. How to compile and run a java program (in command-line)? Code: public class HelloWorld { public static void main(String[] args) { System.out.println("Hellow World!"); } } Output: Hellow World!

3. How to compile and run a java program (in command-line)? public class HelloWorld{ public static void main(String[] args) { System.out.println("Hellow World!"); } } • Install JDK (not JRE) • Compile: javac HelloWorld.java (You will see the bytecode file: HelloWorld.class) • Run: java HelloWorld (not HelloWorld.class here) (All the file names are case-sensitive)

4. How to compile and run a java program (in command-line)?

5. Use variables • Each variable has a type • Use a type keyword to declare a variable • In the most recent grammar, you have to initialize the variable with certain value public class Variables { public static void main(String[] args) { String name = "Haydon"; booleanmale = true; double height = 1.76; //meters System.out.println("Hello World!"); System.out.println("I am: " + name); System.out.println("Am I a male: " + male); System.out.println("My height is: " + height); } }

6. Use variables Code: public class Variables { public static void main(String[] args) { String name = "Haydon"; booleanmale = true; double height = 1.76; //meters System.out.println("Hello World!"); System.out.println("I am: " + name); System.out.println("Am I a male: " + male); System.out.println("My height is: " + height); } } Output: Hello World! I am: Haydon Am I a male: true My height is: 1.76

7. Use operators • There are many operators, their usage is very similar to their counterparts in mathematics. • E.g.: + Addition - Subtraction * Multiplication / Division • There are also many other operators like: modulus(%), increment(++) and so on

8. Use operators Code: public class Operators{ public static void main(String[] args) { double radius = 3.5; double area = 3.1415926 * radius * radius; System.out.println("Area: " + area); } } Output: Area: 38.48450935

9. Use constants • Like a variable, but the value cannot be changed. (You can only initialize it) • It is very useful to replace your “magic numbers” with constants to increase the readability of your code

10. Use constants public class Operators{ public static void main(String[] args) { double radius = 3.5; double area = 3.1415926 * radius * radius; System.out.println("Area: " + area); } } public class Constants { public static void main(String[] args) { final double PI = 3.1415926; double radius = 3.5; double area = PI * radius * radius; System.out.println("Area: " + area); } } Which one is better?

11. Use constants • What will happen, if you use “3.2415” as PI at multiple places, and suddenly find out that it should be “3.1415”? • When you read a 2000 line program, what if you see 8.314? • To avoid those pains, coders use constants.

12. Use methods • Methods are members of classes • You can use the “.” operator to use the public methods public class Methods { public static void main(String[] args) { double value = 2; System.out.println(Math.pow(value, 3)); // System.out.println(Math.sqrt(value)); // System.out.println(Math.round(value)); // round(value) } } 8.0 1.4142135623730951 2

13. If you have more questions, I will be here till 8:30pm