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Java basics

Java basics. In class quiz. What are the rules for an identifier in Java? In what method does a program begin? What is the return type of that method? What parameter(s) does it require? What is the exponentiation operator in Java? How do we produce output in Java?

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Java basics

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  1. Java basics

  2. In class quiz • What are the rules for an identifier in Java? • In what method does a program begin? What is the return type of that method? What parameter(s) does it require? • What is the exponentiation operator in Java? • How do we produce output in Java? • What is operator precedence?

  3. Programming • Problem solving through the use of a computer system • Maxim • You cannot make a computer do something if you do not know how to do it yourself

  4. Software • Program • Sequence of instruction that tells a computer what to do • Execution • Performing the instruction sequence • Programming language • Language for writing instructions to a computer • Major flavors • Machine language or object code • Assembly language • High-level Program to which computer can responddirectly. Each instructionis a binary code thatcorresponds to anative instruction

  5. Software • Program • Sequence of instruction that tells a computer what to do • Execution • Performing the instruction sequence • Programming language • Language for writing instructions to a computer • Major flavors • Machine language or object code • Assembly language • High-level Symbolic languagefor coding machinelanguage instructions

  6. Software • Program • Sequence of instruction that tells a computer what to do • Execution • Performing the instruction sequence • Programming language • Language for writing instructions to a computer • Major flavors • Machine language or object code • Assembly language • High-level Detailed knowledge ofthe machine is notrequired. Uses avocabulary andstructure closer to theproblem being solved

  7. Software • Program • Sequence of instruction that tells a computer what to do • Execution • Performing the instruction sequence • Programming language • Language for writing instructions to a computer • Major flavors • Machine language or object code • Assembly language • High-level Java is a high-levelprogramminglanguage

  8. Software • Program • Sequence of instruction that tells a computer what to do • Execution • Performing the instruction sequence • Programming language • Language for writing instructions to a computer • Major flavors • Machine language or object code • Assembly language • High-level For program to beexecuted it must betranslated

  9. Translation • Translator • Accepts a program written in a source language and translates it to a program in a target language • Compiler • Standard name for a translator whose source language is a high-level language • Interpreter • A translator that both translates and executes a source program

  10. Java translation • Two-step process • First step • Translation from Java to bytecodes • Bytecodes are architecturally neutral object code • Bytecodes are stored in a file with extension .class • Second step • An interpreter translates the bytecodes into machine instructions and executes them • Interpreter is known a Java Virtual Machine or JVM

  11. Task • Display the supposed forecast I think there is a world market for maybe five computers. Thomas Watson, IBM, 1943.

  12. Sample output

  13. DisplayForecast.java // Authors: J. P. Cohoon and J. W. Davidson // Purpose: display a quotation in a console window public class DisplayForecast { // method main(): application entry point public static void main(String[] args) { System.out.print("I think there is a world market for"); System.out.println(" maybe five computers."); System.out.println(" Thomas Watson, IBM, 1943."); } }

  14. DisplayForecast.java // Authors: J. P. Cohoon and J. W. Davidson // Purpose: display a quotation in a console window public class DisplayForecast { // method main(): application entry point public static void main(String[] args) { System.out.print("I think there is a world market for"); System.out.println(" maybe five computers."); System.out.println(" Thomas Watson, IBM, 1943."); } } Three statements make up the action of method main() Method main() is part of class DisplayForecast

  15. DisplayForecast.java // Authors: J. P. Cohoon and J. W. Davidson // Purpose: display a quotation in a console window public class DisplayForecast { // method main(): application entry point public static void main(String[] args) { System.out.print("I think there is a world market for"); System.out.println(" maybe five computers."); System.out.println(" Thomas Watson, IBM, 1943."); } } A method is a named piece of code that performs some action or implements a behavior

  16. DisplayForecast.java // Authors: J. P. Cohoon and J. W. Davidson // Purpose: display a quotation in a console window public class DisplayForecast { // method main(): application entry point public static void main(String[] args) { System.out.print("I think there is a world market for"); System.out.println(" maybe five computers."); System.out.println(" Thomas Watson, IBM, 1943."); } } An application program is required to have a public static void method named main().

  17. DisplayForecast.java // Authors: J. P. Cohoon and J. W. Davidson // Purpose: display a quotation in a console window public class DisplayForecast { // method main(): application entry point public static void main(String[] args) { System.out.print("I think there is a world market for"); System.out.println(" maybe five computers."); System.out.println(" Thomas Watson, IBM, 1943."); } } public, static, and void are keywords. They cannot be used as names public means the method is shareable

  18. DisplayForecast.java // Authors: J. P. Cohoon and J. W. Davidson // Purpose: display a quotation in a console window public class DisplayForecast { // method main(): application entry point public static void main(String[] args) { System.out.print("I think there is a world market for"); System.out.println(" maybe five computers."); System.out.println(" Thomas Watson, IBM, 1943."); } } Consider static and void later

  19. DisplayForecast.java // Authors: J. P. Cohoon and J. W. Davidson // Purpose: display a quotation in a console window public class DisplayForecast { // method main(): application entry point public static void main(String[] args) { System.out.print("I think there is a world market for"); System.out.println(" maybe five computers."); System.out.println(" Thomas Watson, IBM, 1943."); } } Java allows a statement to be made up of multiple lines of text Semicolons delimit one statement from the next

  20. DisplayForecast.java // Authors: J. P. Cohoon and J. W. Davidson // Purpose: display a quotation in a console window public class DisplayForecast { // method main(): application entry point public static void main(String[] args) { System.out.print("I think there is a world market for"); System.out.println(" maybe five computers."); System.out.println(" Thomas Watson, IBM, 1943."); } } A class defines an object form. An object can have methods and attributes Keyword class indicates a class definition follows

  21. DisplayForecast.java // Authors: J. P. Cohoon and J. W. Davidson // Purpose: display a quotation in a console window public class DisplayForecast { // method main(): application entry point public static void main(String[] args) { System.out.print("I think there is a world market for"); System.out.println(" maybe five computers."); System.out.println(" Thomas Watson, IBM, 1943."); } } The class has a name

  22. DisplayForecast.java // Authors: J. P. Cohoon and J. W. Davidson // Purpose: display a quotation in a console window public class DisplayForecast { // method main(): application entry point public static void main(String[] args) { System.out.print("I think there is a world market for"); System.out.println(" maybe five computers."); System.out.println(" Thomas Watson, IBM, 1943."); } } Programs are read by people – make sure they are readable. Use whitespace, comments, and indentation to aidunderstanding

  23. Whitespace DisplayForecast.java // Authors: J. P. Cohoon and J. W. Davidson // Purpose: display a quotation in a console window public class DisplayForecast { // method main(): application entry point public static void main(String[] args) { System.out.print("I think there is a world market for"); System.out.println(" maybe five computers."); System.out.println(" Thomas Watson, IBM, 1943."); } } Whitespace separates program elements Whitespace between program elements is ignored by Java

  24. Three comments DisplayForecast.java // Authors: J. P. Cohoon and J. W. Davidson // Purpose: display a quotation in a console window public class DisplayForecast { // method main(): application entry point public static void main(String[] args) { System.out.print("I think there is a world market for"); System.out.println(" maybe five computers."); System.out.println(" Thomas Watson, IBM, 1943."); } } // indicates rest of the line is a comment Comments are used to document authors, purpose, and program elements

  25. Indentation // Authors: J. P. Cohoon and J. W. Davidson // Purpose: display a quotation in a console window public class DisplayForecast { // method main(): application entry point public static void main(String[] args) { System.out.print("I think there is a world market for"); System.out.println(" maybe five computers."); System.out.println(" Thomas Watson, IBM, 1943."); } } Method main() is part of DisplayForecast Statements are part of method main() Indentation indicates subcomponents

  26. Method main() public static void main(String[] args) { System.out.print("I think there is a world market for"); System.out.println(" maybe five computers."); System.out.println(" Thomas Watson, IBM, 1943."); } • Class System supplies objects that can print and read values • System variable out references the standard printing object • Known as the standard output stream • Variable out provides access to printing methods • print(): displays a value • println(): displays a value and moves cursor to the next line

  27. System.out

  28. Selection

  29. Method main() public static void main(String[] args) { System.out.print("I think there is a world market for"); System.out.println(" maybe five computers."); System.out.println(" Thomas Watson, IBM, 1943."); } • Method print() and println() both take a string parameter • The parameter specifies the value that is to be used in the invocation

  30. Method main() public static void main(String[] args) { System.out.print("I think there is a world market for"); System.out.println(" maybe five computers."); System.out.println(" Thomas Watson, IBM, 1943."); } • The print() statement starts the program output I think there is a world market for░

  31. Method main() public static void main(String[] args) { System.out.print("I think there is a world market for"); System.out.println(" maybe five computers."); System.out.println(" Thomas Watson, IBM, 1943."); } • The first println() statement completes the first line of output I think there is a world market for maybe five computers ░

  32. Method main() public static void main(String[] args) { System.out.print("I think there is a world market for"); System.out.println(" maybe five computers."); System.out.println(" Thomas Watson, IBM, 1943."); } • The second println() statement starts and completes the second line of output I think there is a world market for maybe five computers Thomas Watson, IBM, 1943. ░

  33. Experiments • How do we do the following? • I will do good in my classes.You will do good in your classes. • I'll do good in my classes. • "You will do good in your classes," said Cohoon. • It was a dark and stormy night; the rain fell in torrents--except at occasional intervals, when it was checked by a violent gust of wind which swept up the streets (for it is in London that our scene lies), rattling along the housetops, and fiercely agitating the scanty flame of the lamps that struggled against the darkness.

  34. Computation • Programmers frequently write small programs for computing useful things • Example – body mass index (BMI) • Measure of fitness • Ratio of person’s weight to the square of the person’s height • Weight in is kilograms, height is in meters • Person of interest is 4.5 feet and weighs 75.5 pounds • Metric conversions • Kilograms per pound 0.454 • Meters per foot 0.3046

  35. Common program elements • Type • Set of values along with operators that can manipulate and create values from the set • Primitive types support numeric, character, logical values • double and float • Values with decimals • byte, short, int, long • Integers • char • Characters (considered numeric) • boolean • Logical values • Basic operators • + addition - subtraction • * multiplication / division

  36. Common program elements • Constant • Symbolic name for memory location whose value does not change • KILOGRAMS_PER_POUND • Variable • Symbolic name for memory location whose value can change • weightInPounds

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