Introduction to Java

Transcription

1 Introduction to Java

2 Announcements Programming Assignment #1 Out: Karel the Robot: Due Friday, January 18 at 3:15 PM. Due Sunday, January 20 at 11:59PM. Section assignments given out on Tuesday; you can submit assignments once you have an SL assigned. Assignment review hours: 7:00 9:00PM in Herrin T-175. Didn't sign up? Signups reopen on Tuesday. Not recorded; sorry about that! LaIR hours start tonight!

3 A Farewell to Karel

4 Welcome to Java

5 But First... A Brief History of Digital Computers

6 Image credit:

7 Programming in the 1940s Electrical Device

8 High-Level Languages Image:

9 Programming in the 1950s DO 5 I = 1, 25 Source Deck Computer Compiler Program Deck

10 Programming in the 1950s DO 5 I = 1, 25 Source Deck Computer Compiler Program Deck

11 Programming Now (ish) move(); turnleft(); Source Code Compiler Machine Code

12 Hey! I wrote a program that can draw stick figures! That's great! I wrote a program that makes speech bubbles!

13 Programming Now move(); turnleft(); Compiler Machine Code Object File Source Code Linker Object File Computer

14 Programming Now move(); turnleft(); Compiler Machine Code Object File Source Code Linker Object File Computer

15 Image credit:

16 The Java Model move(); turnleft(); Compiler JAR File.class File Source Code Linker class File Computer Java Computer Virtual Machine

17 Let's See Some Java!

18 The Add2Integers Program public class Add2Integers extends ConsoleProgram { public void run() { println("this program adds two numbers."); int n1 = readint("enter n1: "); int n2 = readint("enter n2: "); int total = n1 + n2; println("the total is " + total + "."); } n1 n2 total } Add2Integers This program adds two numbers. Enter n1: 17 Enter n2: 25 The total is 42. Graphic courtesy of Eric Roberts

19 Variables A variable is a location where a program can store information for later use. Each variable has three pieces of information associated with it: Name: What is the variable called? Type: What sorts of things can you store in the variable? Value: What value does the variable have at any particular moment in time?

20 Variables A variable is a location where a program can store information for later use. Each variable has three pieces of information associated with it: Name: What is the variable called? Type: What sorts of things can you store in the variable? Value: What value does the variable have at any particular moment in time?

21 Variables A variable is a location where a program can store information for later use. Each variable has three pieces of information associated with it: Name: What is the variable called? Type: What sorts of things can you store in the variable? Value: What value does the variable have at any particular moment in time?

22 Variables A variable is a location where a program can store information for later use. Each variable has three pieces of information associated with it: Name: What is the variable called? Type: What sorts of things can you store in the variable? Value: What value does the variable have at any particular moment in time?

23 Variables A variable is a location where a program can store information for later use. int numvoters Each variable has three pieces of information associated with it: Name: What is the variable called? Type: What sorts of things can you store in the variable? Value: What value does the variable have at any particular moment in time?

24 Variables A variable is a location where a program can store information for later use. int numvoters Each variable has three pieces of information associated with it: Name: What is the variable called? Type: What sorts of things can you store in the variable? Value: What value does the variable have at any particular moment in time?

25 Variables A variable is a location where a program can store information for later use. int numvoters Each variable has three pieces of information associated with it: Name: What is the variable called? Type: What sorts of things can you store in the variable? Value: What value does the variable have at any particular moment in time?

26 Variables A variable is a location where a program can store information for later use. int numvoters Each variable has three pieces of information associated with it: Name: What is the variable called? Type: What sorts of things can you store in the variable? Value: What value does the variable have at any particular moment in time?

27 Variables A variable is a location where a program can store information for later use. 137 int numvoters Each variable has three pieces of information associated with it: Name: What is the variable called? Type: What sorts of things can you store in the variable? Value: What value does the variable have at any particular moment in time?

28 Variables A variable is a location where a program can store information for later use. 137 int numvoters Each variable has three pieces of information associated with it: Name: What is the variable called? Type: What sorts of things can you store in the variable? Value: What value does the variable have at any particular moment in time?

29 Variable Names Legal names for variables begin with a letter or an underscore (_) consist of letters, numbers, and underscores, and aren't one of Java's reserved words. x 7thHorcrux Harry Potter noordinaryrabbit lots_of_underscores w LOUD_AND_PROUD that'sacoolname true C_19_H_14_O_5_S

30 Variable Names Legal names for variables begin with a letter or an underscore (_) consist of letters, numbers, and underscores, and aren't one of Java's reserved words. x 7thHorcrux Harry Potter noordinaryrabbit lots_of_underscores w LOUD_AND_PROUD that'sacoolname true C_19_H_14_O_5_S

31 Variable Names Legal names for variables begin with a letter or an underscore (_) consist of letters, numbers, and underscores, and aren't one of Java's reserved words. x 7thHorcrux Harry Potter noordinaryrabbit lots_of_underscores w LOUD_AND_PROUD that'sacoolname true C_19_H_14_O_5_S

32 Variable Names Legal names for variables begin with a letter or an underscore (_) consist of letters, numbers, and underscores, and aren't one of Java's reserved words. x 7thHorcrux Harry Potter noordinaryrabbit lots_of_underscores w LOUD_AND_PROUD that'sacoolname true C_19_H_14_O_5_S

33 Variable Names Legal names for variables begin with a letter or an underscore (_) consist of letters, numbers, and underscores, and aren't one of Java's reserved words. x 7thHorcrux Harry Potter noordinaryrabbit lots_of_underscores w LOUD_AND_PROUD that'sacoolname true C_19_H_14_O_5_S

34 Variable Names Legal names for variables begin with a letter or an underscore (_) consist of letters, numbers, and underscores, and aren't one of Java's reserved words. x 7thHorcrux Harry Potter noordinaryrabbit lots_of_underscores w LOUD_AND_PROUD that'sacoolname true C_19_H_14_O_5_S

35 Variable Names Legal names for variables begin with a letter or an underscore (_) consist of letters, numbers, and underscores, and aren't one of Java's reserved words. x 7thHorcrux Harry Potter noordinaryrabbit lots_of_underscores w LOUD_AND_PROUD that'sacoolname true C_19_H_14_O_5_S

36 Variable Names Legal names for variables begin with a letter or an underscore (_) consist of letters, numbers, and underscores, and aren't one of Java's reserved words. x noordinaryrabbit lots_of_underscores w LOUD_AND_PROUD C_19_H_14_O_5_S

37 Variable Naming Conventions You are free to name variables as you see fit, but there are conventions. Names are often written in lower camel case: capitalizeallwordsbutthefirst Choose names that describe what the variable does. If it's a number of votes, call it numberofvotes, numvotes, votes, etc. Don't call it x, volumecontrol, or severussnape

38 Variable Naming Conventions You are free to name variables as you see fit, but there are conventions. Names are often written in lower camel case: capitalizeallwordsbutthefirst Choose names that describe what the variable does. If it's a number of votes, call it numberofvotes, numvotes, votes, etc. Don't call it x, volumecontrol, or severussnape

39 Variable Naming Conventions You are free to name variables as you see fit, but there are conventions. Names are often written in lower camel case: capitalizeallwordsbutthefirst Choose names that describe what the variable does. If it's a number of votes, call it numberofvotes, numvotes, votes, etc. Don't call it x, volumecontrol, or severussnape

40 Variable Naming Conventions You are free to name variables as you see fit, but there are conventions. Names are often written in lower camel case: capitalizeallwordsbutthefirst Choose names that describe what the variable does. If it's a number of voters, call it numberofvoters, numvoters, voters, etc. Don't call it x, volumecontrol, or severussnape

41 Types The type of a variable determines what can be stored in it. Java has several primitive types that it knows how to understand: int: Integers. double: Real numbers. char: Characters (letters, punctuation, etc.) boolean: Logical true and false.

42 Types The type of a variable determines what can be stored in it. Java has several primitive types that it knows how to understand: int: Integers. double: Real numbers. char: Characters (letters, punctuation, etc.) boolean: Logical true and false.

43 Types The type of a variable determines what can be stored in it. Java has several primitive types that it knows how to understand: int: Integers. double: Real numbers. char: Characters (letters, punctuation, etc.) boolean: Logical true and false.

44 Types The type of a variable determines what can be stored in it. Java has several primitive types that it knows how to understand: int: Integers. double: Real numbers. char: Characters (letters, punctuation, etc.) boolean: Logical true and false.

45 Types The type of a variable determines what can be stored in it. Java has several primitive types that it knows how to understand: int: Integers. (counting) double: Real numbers. char: Characters (letters, punctuation, etc.) boolean: Logical true and false.

46 Types The type of a variable determines what can be stored in it. Java has several primitive types that it knows how to understand: int: Integers. (counting) double: Real numbers. (measuring) char: Characters (letters, punctuation, etc.) boolean: Logical true and false.

47 Types The type of a variable determines what can be stored in it. Java has several primitive types that it knows how to understand: int: Integers. (counting) double: Real numbers. (measuring) boolean: Logical true and false.

48 Types The type of a variable determines what can be stored in it. Java has several primitive types that it knows how to understand: int: Integers. (counting) double: Real numbers. (measuring) boolean: Logical true and false. char: Characters and punctuation.

49 Values 137 int numvotes double fractionvoting double fractionyes

50 Declaring Variables

51 Declaring Variables public void run() { }

52 Declaring Variables public void run() { double ourdouble = ; }

53 Declaring Variables public void run() { double ourdouble = ; ourdouble }

54 Declaring Variables public void run() { double ourdouble = ; ourdouble The The syntax syntax for for declaring declaring aa variable variable with with an an initial initial value value isis type typename name==value; value; }

55 Declaring Variables ourdouble public void run() { double ourdouble = ; int ourint = 137; }

56 Declaring Variables ourdouble public void run() { double ourdouble = ; int ourint = 137; 137 ourint }

57 Declaring Variables ourdouble public void run() { double ourdouble = ; int ourint = 137; int anotherint; 137 ourint }

58 Declaring Variables ourdouble public void run() { double ourdouble = ; int ourint = 137; int anotherint; 137 ourint anotherint }

59 Declaring Variables ourdouble public void run() { double ourdouble = ; int ourint = 137; int anotherint; 137 Variables Variables can can be be declared declared without without an an initial initial value: value: ourint type typename; name; anotherint }

60 Declaring Variables ourdouble public void run() { double ourdouble = ; int ourint = 137; int anotherint; anotherint = 42; 137 ourint anotherint }

61 Declaring Variables ourdouble public void run() { double ourdouble = ; int ourint = 137; int anotherint; anotherint = 42; 137 ourint 42 anotherint }

62 Declaring Variables ourdouble public void run() { double ourdouble = ; int ourint = 137; int anotherint; anotherint = 42; 137 ourint An An assignment assignment statement statement has has the the form form 42 variable variable==value; value; anotherint } This This stores stores value value in in variable. variable.

63 Declaring Variables ourdouble public void run() { double ourdouble = ; int ourint = 137; int anotherint; anotherint = 42; 137 ourint ourint = 13; 42 anotherint }

64 Declaring Variables ourdouble public void run() { double ourdouble = ; int ourint = 137; int anotherint; anotherint = 42; 13 ourint ourint = 13; 42 anotherint }

65 Declaring Variables ourdouble public void run() { double ourdouble = ; int ourint = 137; int anotherint; anotherint = 42; 13 ourint ourint = 13; 42 anotherint }

66 Declaring Variables ourdouble public void run() { double ourdouble = ; int ourint = 137; int anotherint; anotherint = 42; 13 ourint ourint = 13; ourint = ourint + 1; 42 anotherint }

67 Declaring Variables ourdouble public void run() { double ourdouble = ; int ourint = 137; int anotherint; anotherint = 42; 14 ourint ourint = 13; ourint = ourint + 1; 42 anotherint }

68 Declaring Variables ourdouble public void run() { double ourdouble = ; int ourint = 137; int anotherint; anotherint = 42; 14 ourint ourint = 13; ourint = ourint + 1; 42 anotherint }

69 Declaring Variables ourdouble public void run() { double ourdouble = ; int ourint = 137; int anotherint; anotherint = 42; 14 ourint ourint = 13; ourint = ourint + 1; 42 anotherint = ourint; anotherint }

70 Declaring Variables ourdouble public void run() { double ourdouble = ; int ourint = 137; int anotherint; anotherint = 42; 14 ourint ourint = 13; ourint = ourint + 1; 14 anotherint = ourint; anotherint }

71 Declaring Variables ourdouble public void run() { double ourdouble = ; int ourint = 137; int anotherint; anotherint = 42; 14 ourint ourint = 13; ourint = ourint + 1; 14 anotherint = ourint; anotherint }

72 Declaring Variables ourdouble public void run() { double ourdouble = ; int ourint = 137; int anotherint; anotherint = 42; 14 ourint ourint = 13; ourint = ourint + 1; 14 anotherint = ourint; ourint = 1258; anotherint }

73 Declaring Variables ourdouble public void run() { double ourdouble = ; int ourint = 137; int anotherint; anotherint = 42; 1258 ourint ourint = 13; ourint = ourint + 1; 14 anotherint = ourint; ourint = 1258; anotherint }

74 Declaring Variables ourdouble public void run() { double ourdouble = ; int ourint = 137; int anotherint; anotherint = 42; 1258 ourint ourint = 13; ourint = ourint + 1; 14 anotherint = ourint; ourint = 1258; anotherint }

75 The Add2Integers Program public class Add2Integers extends ConsoleProgram { public void run() { println("this program adds two numbers."); int n1 = readint("enter n1: "); int n2 = readint("enter n2: "); int total = n1 + n2; println("the total is " + total + "."); } n1 n2 total } Add2Integers This program adds two numbers. Enter n1: 17 Enter n2: 25 The total is 42. Graphic courtesy of Eric Roberts

76 The Add2Integers Program public class Add2Integers extends ConsoleProgram { public void run() { println("this program adds two numbers."); int n1 = readint("enter n1: "); int n2 = readint("enter n2: "); int total = n1 + n2; println("the total is " + total + "."); } n1 n2 total } Add2Integers This program adds two numbers. Enter n1: 17 Enter n2: 25 The total is 42. Graphic courtesy of Eric Roberts