CIS3023: Programming Fundamentals for CIS Majors II Summer 2010 Ganesh Viswanathan Programming in JAVA – II (A Whirlwind Tour of Java) Course Lecture Slides 17 May 2010

JAVA Duke, the JAVA mascot Java 1.0 was first released by Sun Microsystems in Java became popular for web programming. "Write Once, Run Anywhere" (WORA) philosophy. Key design principles: -Platform independence -Security -Stability

How Java works!

Programming in JAVA – I Basic concepts in Java Values Variables Complex data/objects Methods Expressions Conditionals Loops

Programming in JAVA English to JAVA translation: Piece of data: value Kind of data: type Place to store a value: variable Structured group of variables: object Kind of object: class Object of a particular class: class instance Variable belonging to an object: instance variable

Programming in JAVA Values and Types : All data values in Java have a type The type of a value determines: Allowed operations Memory representation Allowed operations Conversion to other types Allowed operations Types are program invariants Help to catch errors Default initial values (if omitted) are based on type

Programming in JAVA Primitive Types: EIGHT basic pre-defined types: values on which Java can operate directly. byte, short, int, long, float, double, boolean, char Plus, special support for character strings - using java.lang.String class

Programming in JAVA - II Numeric Types in Java are characterized by their size (how much memory they occupy) Integral types Floating point types SizeRange (inclusive) byte1 byte-128: 127 short2 bytes-32,768: 32,767 char2 bytes0: 65,535 int4 bytes-2 31 : long8 bytes-2 63 : float4 bytes : ( )·2 127 double8 bytes : ( )·2 1023

Strings Built-in non-primitive type “String” String s1 = “my string”; Strings are sequence of characters “UF” “Pugh Hall” string literals + means concatenation “Pugh” + “ ” + “Hall” => “Pugh Hall” Automatic conversion of numbers to strings “Go” “UF” => Go2UF Text in a String is immutable

Variables Variables store values myScore = 100; isRaining = true; monthlySalary = ; PI = ; myName = “Buzz Aldrin”; All variables must be declared!

Variables Assignment statement “ = “ int myScore = 100; boolean isRaining = true; float monthlySalary = ; double PI = ; String myName = “Buzz Aldrin”; Variables must store values of the correct type myScore = true; isRaining = 1; Prevent nonsensical calculations

Initializing Variables Preferred usage: Combine declaration and value initialization in one step: String myCar = “Mustang”; Boolean isRaining = true; Default initial values (unless specified) are based on type.

Default type values Default initial values (unless explicitly specified) are based on type. TypeDefault value byte0 short0 int0 long0L float0.0f double0.0d char'\u0000' String (or any Object) null booleanfalse

Methods A set of instructions referenced by a name that can be called whenever required public class Report{ public static void main(String args[]){ printHelloWorld(); } //simple print method public static void printHelloWorld(){ System.out.println(“Hello World!”); }

Demystifying the main( ) method public static void main (String args[ ]) “The boss function!” : When you execute a class with the Java interpreter, the runtime system starts by calling the class's main() method. The main() method then calls all the other methods required to run your application. The keyword public indicates that the method can be called by any object. The keyword static indicates that the method is a class method, which can be called without the requirement to instantiate an object of the class. The keyword void indicates that the method doesn't return any value. String args[] - “an array of strings”: Mechanism through which the runtime system passes command line arguments to your application.

“Parameters” vs “Arguments” Parameters specify data that must be provided in an invocation public getName (String ufid, int year) { … searchUFID = ufid; searchYear=year; … } Arguments are the actual values supplied to a method String name = getName (“ ”, 2010);

Naming Conventions KindIdentifier ClassGradeBook VariableinitialGrade ConstantMAXIMUM_GRADE MethodgetStudentGrade

Java Expressions Compute values of different types Boolean values: 10>5 Numeric values: 2+3, 5%2 String values: “Pugh”+” Hall” Object values: new GradeBook();

Control Flow Statements Use a condition to choose which action to take. If, Else If, Else (Multi-way decisions, Nested decisions) Switch-case While, Do-While For /java/nutsandbolts/flow.html /java/nutsandbolts/flow.html

{ if (latitude > 0) animal = "polar bear"; else animal = "penguin"; } { if (latitude > 0) animal = "polar bear"; else animal = "penguin"; } Control Flow Statements If, Else-If, Else (Multi-way decisions, Nested decisions) public String dominant() { String animal; if (isFrigid()) else animal = “cat"; return animal; } public String transport() { … if (isFrigid()) return "skis"; else if (isTropical()) return "surfboard"; else return "bicycle"; }

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