UMass Lowell Computer Science Java and Distributed Computing Prof. Karen Daniels Fall, 2000 Lecture 5 Java Fundamentals Fri. 9/15/00

Homework #1, Part 1 Due today at start of lecture.

Homework #1, Part 2 Mon, 9/18 “Hello World” programming (application and applet) Homework is due at the start of lecture on the due date. Note: If you want to use Swing on HW#1 in UML CS UNIX environment, use the Java version located in: /usr/opt/java122/bin /usr/opt/java122/bin/javac /usr/opt/java122/bin/javac /usr/opt/java122/bin/java /usr/opt/java122/bin/java Entire class will transition to this Java version starting with HW#2. Entire class will transition to this Java version starting with HW#2. This Java version is on the saturn CS machine.This Java version is on the saturn CS machine. If you are using a workstation (not just an X-terminal), remotely log into saturn so you can access the Java version on saturn. Otherwise, you will default to the Java version that is on that workstation. If you are using a workstation (not just an X-terminal), remotely log into saturn so you can access the Java version on saturn. Otherwise, you will default to the Java version that is on that workstation. Note: When testing an applet in the UML CS UNIX environment, be sure to set the UNIX DISPLAY environment variable appropriately.

Homework #1, Part 2 (continued) Homework is due at the start of lecture on the due date. To submit your files electronically, use the UNIX submit command Example for 3 files: Example for 3 files: submit kdaniels hw1 filename.java filename.class filename.html submit kdaniels hw1 filename.java filename.class filename.html You’ll submit 5 files for HW#1, part 2: 2 for application, 3 for applet You’ll submit 5 files for HW#1, part 2: 2 for application, 3 for applet Submission deadline is 9:30 a.m. on Monday, 18 September Submission deadline is 9:30 a.m. on Monday, 18 September I have now set it up to allow multiple submissions before the deadline I have now set it up to allow multiple submissions before the deadline Bring a paper printout of your code to give to me at start of Monday’s lecture Bring a paper printout of your code to give to me at start of Monday’s lecture

Java Fundamentals ä 1: Java fundamentals ä applets, applications, data types, control structures, OO programming, files ä 2: Advanced Java concepts & Java support for distributed computing ä GUI/events, graphics, exceptions, advanced data structures, threads/ multithreading, RMI ä 3: Distributed computing using a sample Java- based environment: Jini

Syllabus for Part 1 of the Course Closed book; Worth 15% of grade

Why Java & Distributed Computing? ä Platform independence helps with heterogeneous hardware, software challenge ä Built-in support for: ä Multithreading: “concurrent” multiple activities ä Client-Server computing: servlets, JDBC ä Remote Method Invocation (RMI): method calls across network ä Networking: socket-based communication views networking like file I/O For insight into the original Java vision, see the original Java whitepaper by James Gosling at:

Introduction to Java Applications ä Java application is executed using the Java interpreter (but not inside browser like an applet) ä Application begins execution in main( ) ä main( ) is static method inside class ä no convenient input from command line ä System.exit(0); // required to clean up // after GUI/graphics // after GUI/graphics // Save this in file Welcome1.java public class Welcome1{ public static void main( String args[] ) public static void main( String args[] ) { System.out.println( "Java is fun!" ); System.out.println( "Java is fun!" ); }} javac Welcome1.java java Welcome1 Welcome1.class Welcome1.java

javac Welcome1Applet.java appletviewer Welcome1Applet.html Introduction to Java Applets ä Java applet is executed inside a WWW browser (or appletviewer) using a Java interpreter that is inside the browser. Welcome1Applet.class Welcome1Applet.java Welcome1Applet.html // Save this file in Welcome1Applet.java import java.applet.*; import java.awt.*; public class Welcome1Applet extends Applet{ public void paint(Graphics g) public void paint(Graphics g) { g.drawString( "Java is fun!”, 25, 50 ); g.drawString( "Java is fun!”, 25, 50 ); }} <HTML> </APPLET></HTML> Save this file in Welcome1Applet.html

Introduction to Java Applets (continued) ä Order of (a subset of) applet method invocations: ä init( ) ä start( ) ä paint( )

C to C++ to Java: At a Glance C Primitive Data Types Arrays Struct, Union, Enum Preprocessor Directives OperatorsExpressions Control Statements FunctionsPointers Dynamic Memory Mgt File I/O Exception Handling JavaC++ Primitive Data Types Arrays Struct, Union, Enum Preprocessor Directives OperatorsExpressions Control Statements FunctionsPointers Dynamic Memory Mgt File I/O Exception Handling Classes Multiple Inheritance PolymorphismTemplates uu Primitive Data Types Arrays OperatorsExpressions Control Statements Dynamic Memory Mgt File I/O Exception Handling Classes, Interfaces Inheritance InheritancePolymorphism Support for DBs, networks, GUIs, events, graphics, threads, libraries Procedural, Compiled Language Procedural/OO, Compiled Language OO, Interpreted Language

Java Variables ä Two types: ä primitive data type variable (a.k.a. variable) ä always passed by value ä initialized by default to 0 if numeric; false if boolean ä except for local variables ä value is constant if final keyword is used ä reference variable (a.k.a. reference) ä refers to memory location of object ä always passed by reference ä initialized by default to null

Java Primitive Data Types

Java Array Class ä Declarations: ä One-dimensional: ä int c [ ]; c = new int [8]; ä int c [ ] = new int [8]; ä final int ARRAY_SIZE = 8; int c [ ] = new int [ARRAY_SIZE]; ä int c [ ] = { 32, 44, 6, 7, -1, 25, 88, -31 }; ä Multi-dimensional (e.g. 2): ä int c[ ][ ] = { {32, 44, 6, 7 }, {-1, 25, 88, -31} }; ä int c[ ][ ] = new int[2][4]; ä int c[ ][ ] = new int[2][ ]; // allocate rows for non-rectangular array ä c[0] = new int[3]; // allocate columns for row 0 ä c[1] = new int[4]; // allocate columns for row 1 ä Knows its own length! (e.g. c.length) ä Bounds are checked for you!

Java String Class (basics) ä String is a series of characters treated as a single unit ä Declarations and Constructors: ä String s; // empty string for now -- its length is 0 ä s = new String(); // String() is null constructor. It yields an empty // string for now whose length is 0 ä s = new String(“hello”); // initializes s to “hello” ä String s = “hello”; // initializes s to “hello” ä s2 = new String (s1); // copy constructor ä String s = “hello” + “ world”; // String concatenation ä s1.equals (s2); // tests equality of contents ä s1 = = s2 // tests if both refer to same object in memory ä Knows its own length! (e.g. s.length) ä Array of Strings: String Pets[ ] = {“dog”, “cat”, “fish”};

Some Java Operators [Deitel, p. 271; complete list is in Appendix C] Precedence: Operator higher up the chart is evaluated before operator lower down the chart Associativity: Order of evaluation for operators of equal precedence

Expressions ä Sequence of operators and operands that specifies a computation ä May result in a value (e.g., 123, true) ä May cause side-effects (e.g., change a value) ä Compound expressions (e.g., (a*b)+c)) ä Includes literals (numbers or strings)

Java Expression BNF expression ::= numeric_expression | testing_expression | logical_expression | string_expression | bit_expression | casting_expression | creating_expression | literal_expression | "null" | "super" | "this" | identifier | ( "(" expression ")" ) | ( expression ( ( "(" [ arglist ] ")" ) | ( "[" expression "]" ) | ( "." expression ) | ( "," expression ) | ( "instanceof" ( class_name | interface_name ) ) ) ) From Enseignement/analyseinfo/BNFweb.html

Statements ä Smallest “executable” unit ä Declaration statements ä Control statements ä Assignment statements ä Method invocation ä Compound statement (block) ä Semicolon-separated list of statements ä Enclosed in “curly” brackets { } ä Deitel calls it a ‘block’ only if it has declarations of its own

Java Abstract Windowing Toolkit GUI Components (from java.awt package) ä java.awt.Graphics (see list on p ) ä Given an object g of Graphics class: ä g.setColor( Color.red ); // Sets current drawing color to red ä g.drawString(“hello”, 200, 25); // Draws String starting at (200,25) ä g.drawLine(20, 28, 40, 10 ); // Draws line from (20,28) to (40,10) ä g.fillRect(100, 5, 20, 15); // Draws filled rectangle whose upper left // corner is at (100, 5). Width = 20. Height = 15 // corner is at (100, 5). Width = 20. Height = 15 ä g.drawOval(60, 9, 20, 13); // Draws oval whose bounding box upper left // corner is at (60, 9). Width = 20. Height = 13 // corner is at (60, 9). Width = 20. Height = 13 (0,0)x y hello usescurrentcolor

Java Swing GUI Components (from javax.swing package) ä javax.swing.JOptionPane ä Dialog box ä message ä error ä information ä warning ä question ä plain ä input ä javax.swing.JTextArea ä javax.swing.JScrollPane

Homework 1 Fri, 9/8 Fri, 9/15 Part 1 Mon, 9/18 Part 2 Mon, 9/18 Part 2 2Fri, 9/15 Fri, 9/22 Part 1 & Part 2 HW# Assigned Due Content Homework is due at the start of lecture on the due date.