The 1 st tutoring session of CSc2310 Fall, 2012
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Transcript of The 1 st tutoring session of CSc2310 Fall, 2012
The 1st tutoring session of CSc2310Fall, 2012
Haidong Xue
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!");
}}
Hellow World!
Code:
Output:
How to compile and run a java program (in command-line)?
• 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)
public class HelloWorld {public static void main(String[] args) {
System.out.println("Hellow World!");
}}
How to compile and run a java program (in command-line)?
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 valuepublic class Variables {
public static void main(String[] args) {String name = "Haydon";boolean male = true;double height = 1.76; //metersSystem.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);
}}
Use variablespublic class Variables {
public static void main(String[] args) {String name = "Haydon";boolean male = true;double height = 1.76; //metersSystem.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);
}}
Hello World!I am: HaydonAm I a male: trueMy height is: 1.76
Code:
Output:
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
Use operatorspublic class Operators{
public static void main(String[] args) {double radius = 3.5;double area = 3.1415926 * radius * radius;System.out.println("Area: " + area);
}}
Area: 38.48450935
Code:
Output:
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
Use constantspublic 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?
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.
Use methods• Methods are members of classes• You can use the “.” operator to use the public
methodspublic 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)
}}
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If you have more questions, I will be here till 8:30pm