Lectures / lecture2_1
.pdfJava Programming Language
Lecture 2.
Class. Class Design. Methods. Variables. Data types.
Brodyagina Mariya
Symbols Used in Defining a Java
Source
– Braces
– Parentheses
–Semicolons 
–Commas 
–Single quotation marks
– Double quotation marks
– Single-line comment
Class Structure
package <package_name>;
import <other_packages>;
public class ClassName { <variables(also known as fields)>;
<constructor method(s)>;
<other methods>;
}
A Simple Class
A simple Java class with a main method:
public class Simple {
public static void main(String args[]){
}
}
Syntax for declaring a class:
[modifiers] class class_identifier
Java Naming Conventions
Class names are nouns in
upper camel case.
1 public class CreditCard {
2public final int VISA = 5001;
3public String accountName;
4public String cardNumber;
5public Date expDate;
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public double getCharges(){ |
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// ... |
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} |
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Constants should be declared in all uppercase. letters
Variable names are short but meaningful in lower camel case.
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public void disputeCharge(String chargeId, float amount){ |
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// ... |
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} |
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Methods should be verbs, in |
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lower camel case. |
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Comments
// single-line comment /* single-line comment */ /*
* block comment */
statement; // trailing comment
Javadoc comments:
/**
* Javadoc comment */
/** Javadoc comment */
Quiz
Select the class declaration that adheres to the class-naming guidelines.
a.class Shirt
b.public Class 501Pants c.public Shirt
d.public Class Pants
A Simple Java Class: Employee
A Java class is often used to represent a concept.
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package com.example.domain; |
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public class Employee { class declaration |
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public int empId; |
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public String name; |
fields |
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public String ssn; |
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public double salary; |
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public Employee () { a constructor |
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} |
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public int getEmpId () { a method |
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return empId; |
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} |
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14 }
Uses of Variables
–Holding unique data for an object instance
–Assigning the value of one variable to another
–Representing values within a mathematical expression
–Printing the values to the screen
–Holding references to other objects
Naming a Variable
•Rules:
–Variable identifiers must start with either an uppercase or lowercase letter, an underscore (_), or a dollar sign ($).
–Variable identifiers cannot contain punctuation, spaces, or dashes.
–Java technology keywords cannot be used.