Java Methods

1
Console Output
2
Objectives

• Writing a Java program.
• How to send output to the command line console.
• Learn about escape sequences.
• Learn how to compile, debug, and execute a Java
  program.

3
Console Output

• In Java, console output is achieved by calling
  System.out.print or System.out.println.
• The data to be output is given as an argument in
  parentheses.
• System.out.println(Blackjack)
• Every invocation of println ends a line of
  output.
• Blackjack
• _

4
println Versus print

• The print method is like println, except that it
  does not end a line
• With println, the next output goes on a new line
• With print, the next output goes on the same line

5
The print Method

• System.out.print(Hello )
• System.out.print(World)

6
The print Method

• System.out.print(Hello )
• System.out.print(World)
• Output
• HelloWorld

7
The print Method

• System.out.print(Hello )
• System.out.print(World)

8
The print Method

• System.out.print(Hello )
• System.out.print(World)
• Output
• Hello World

9
The println Method

• System.out.println(Hello)
• System.out.println(World)

10
The println Method

• System.out.println(Hello)
• System.out.println(World)
• Output
• Hello
• World

11
The Symbol
21 is a Blackjack 7 7 is lucky Lucky
number 34

• A plus sign is used to connect more than one item
• System.out.println(21 is a Blackjack)
• System.out.println(3 4)
• System.out.println(3 4 is lucky)
• System.out.println(Lucky number 3 4)

12
Other Math Symbol
6 Error the symbol can not be used with
Strings 7 is lucky Error the symbol can
not be used with Strings 3

• Be careful when using other math symbols.
• System.out.println(3 2)
• System.out.println(3 Hello World)
• System.out.println(11 4 is lucky)
• System.out.println(Lucky number 11 - 4)
• System.out.println(15 / 4)

13
Escape Sequences

• Escape sequences are used to print characters
  that are non-printable. Escape sequences always
  begin with a \ (backslash) character.
• Common Escape sequences
• \n new line
• \ quote symbol
• \t tab
• \\ - backslash

14
Escape Sequences (Cont)
System.out.println(Hello\nWorld)

• Output
• Hello
• World

15
Escape Sequences (Cont)

• System.out.println(Hello\tWorld)

Output Hello World
16
Escape Sequences (Cont)

• System.out.println(\Hello\tWorld\)

Output Hello World
17
Sequential Programming
The order in which statements occur is important.

• Normally program statements execute from top to
  bottom.
• This is called sequential control. Sequential
  control is the default control structure.
• There are other control structures that we will
  discuss later.

18
Sequential Programming (cont)

• What will be output by the following program
  segment?
• System.out.print(Chester )
• System.out.print(Nimitz)

Output Chester Nimitz
19
Sequential Programming (cont)

• Now what will be output by the following program
  segment?
• System.out.print(Chester\nNimitz)

Output Chester Nimitz
20
Sequential Programming (cont)

• Now what will be output by the following program
  segment?
• System.out.println(Chester\\Nimitz)

Output Chester\Nimitz
21
Sequential Programming (cont)

• Keep in mind as you are programming that where
  you place a statement determines when it will be
  executed.
• SEQUENTIAL CONTROL

22
How Does String Concatenation Work?
23
String Concatenation
Here is a typical print statement.

• System.out.print(Hello 1 2)

24
String Concatenation (cont)

• System.out.print(Hello 1 2)

Hello 1
25
String Concatenation (cont)

• System.out.print(Hello 1 2)

Hello 1
Hello 12
26
String Concatenation (cont)
Here is another typical print statement.

• System.out.print(1 2 Hello)

27
String Concatenation (cont)

• System.out.print(1 2 Hello)

3
28
String Concatenation (cont)

• System.out.print(1 2 Hello)

3
3 Hello
29
String Concatenation (cont)
Here is another typical print statement.

• System.out.print(Hello 3 2)

30
String Concatenation (cont)

• System.out.print(Hello 3 2)

Multiplication has a higher precedence than
addition!
31
String Concatenation (cont)

• System.out.print(Hello 3 2)

6
32
Sequential Programming (cont)

• System.out.print(Hello 3 2)

6
Hello 6
33
String Concatenation (cont)
Here is another typical print statement.

• System.out.print(Hello 6 - 4)

34
String Concatenation (cont)

• System.out.print(Hello 6 - 4)

Hello 6
35
String Concatenation (cont)

• System.out.print(Hello 6 - 4)

Hello 6
Compile Time Error operator - can not be applied
to String, int
36
String Concatenation (cont)
How can we fix this problem?

• System.out.print(Hello 6 - 4)

37
String Concatenation (cont)
Use parantheses!

• System.out.print(Hello (6 - 4))

38
Sequential Programming (cont)

• System.out.print(Hello (6 - 4))

2
39
Sequential Programming (cont)

• System.out.print(Hello (6 - 4))

2
Hello 2
40
Java
Object Oriented Programming
Top Down Design
41
Top Down Design

• Start JCreator.
• Create a new file called Lab01.java.
• Save the new file in your Lab01 folder.

42
Creating A Java Class File
43
Creating A Java Class File (cont)
44
Creating A Java Class File (cont)
45
Creating A Java Class File (cont)
46
Creating A Java Class File (cont)
47
Creating A Java Class File (cont)
Class names should always begin with an uppercase
letter.
48
Creating A Java Class File (cont)
Click this button to set the location.
49
Creating A Java Class File (cont)
50
Creating A Java Class File (cont)
51
Declaring A Java Class

• public class Lab01

52
Declaring A Java Class

• public class Lab01

53
Declaring A Java Class

• public class Lab01

54
Declaring A Java Class

• public class Lab01

55
The main Method

• In Java, you need to have a method named main in
  at least one class.
• This method must appear within a class, but it
  can be any class.
• A class containing a main method is a program.
  Every program has a main method but not every
  class is a program.

56
The main Method (cont)

• public class Lab01
• public static void main(String args)

Curly brackets are used to define
block statements. Methods, like classes,
are block statements and must begin and end with
a set of curly brackets.
57
The main Method (cont)

• public class Lab01
• public static void main(String args)

58
The main Method (cont)

• public class Lab01
• public static void main(String args)
• System.out.println(Main Method!)

59
Compiling A Java Class File
60
Compiling A Java Class File
61
Running A Java Program
62
Running A Java Program
63
The main Method (cont)

• public class Lab01
• public static void main(String args)
• System.out.println(Main Method!)
• public void output()
• System.out.println(Hello World)

64
The main Method (cont)
Run the program

• public class Lab01
• public static void main(String args)
• System.out.println(Main Method!)
• public void output()
• System.out.println(Hello World)

65
The main Method (cont)
66
The main Method (cont)

• public class Lab01
• public static void main(String args)
• System.out.println(Main Method!)
• public void output()
• System.out.println(Hello World)

67
The main Method (cont)

• public class Lab01
• public static void main(String args)
• System.out.println(Main Method!)
• public void output()
• System.out.println(Hello World)

68
The main Method (cont)

• public class Lab01
• public static void main(String args)
• public void output()
• System.out.println(Hello World)

69
The main Method (cont)

• public class Lab01
• public static void main(String args)
• public void output()
• System.out.println(Hello World)

70
The main Method (cont)

• public class Lab01
• public static void main(String args)
• output()
• public void output()
• System.out.println(Hello World)

71
The main Method (cont)
72
The main Method (cont)
73
The main Method (cont)
74
The main Method (cont)
75
The main Method (cont)
76
The main Method (cont)

• Static methods are class methods. Non-static
  methods are instance methods. Class methods can
  not call instance methods however instance
  methods can call class methods. More on this
  topic later.
• To be able to call output we need an instance of
  the class Lab01.

77
The main Method (cont)

• public class Lab01
• public static void main(String args)
• output()
• public void output()
• System.out.println(Hello World)

78
The main Method (cont)
lab is an object. An object is an instance of a
class.

• public class Lab01
• public static void main(String args)
• Lab01 lab new Lab01()
• public void output()
• System.out.println(Hello World)

79
The main Method (cont)

• public class Lab01
• public static void main(String args)
• Lab01 lab new Lab01()
• lab.output()
• public void output()
• System.out.println(Hello World)

80
Run The Program
81
The main Method (cont)

• public class Lab01
• public static void main(String args)
• Lab01 lab new Lab01()
• lab.output()
• public void output()
• System.out.println(Hello\nWorld)

82
The main Method (cont)

• public class Lab01
• public static void main(String args)
• Lab01 lab new Lab01()
• lab.output()
• public void output()
• System.out.println(Hello\\World)

83
The main Method (cont)

• public class Lab01
• public static void main(String args)
• Lab01 lab new Lab01()
• lab.output()
• public void output()
• System.out.println(Hello World 1 2)

84
The main Method (cont)

• public class Lab01
• public static void main(String args)
• Lab01 lab new Lab01()
• lab.output()
• public void output()
• System.out.println(1 2 Hello World)

85
Control Structures
86
Sequential ControlBranchingConditionsLooping
Control Structures
87
How The Program Executes.
88
The main Method (cont)

• public class Lab01
• public static void main(String args)
• Lab01 lab new Lab01()
• lab.output()
• public void output()
• System.out.println(1 2 Hello World)

89
The main Method (cont)

• public class Lab01
• public static void main(String args)
• Lab01 lab new Lab01()
• lab.output()
• public void output()
• System.out.println(1 2 Hello World)

90
The main Method (cont)

• public class Lab01
• public static void main(String args)
• Lab01 lab new Lab01()
• lab.output()
• public void output()
• System.out.println(1 2 Hello World)

91
The main Method (cont)

• public class Lab01
• public static void main(String args)
• Lab01 lab new Lab01()
• lab.output()
• public void output()
• System.out.println(1 2 Hello World)

92
The main Method (cont)

• public class Lab01
• public static void main(String args)
• Lab01 lab new Lab01()
• lab.output()
• public void output()
• System.out.println(1 2 Hello World)

93
The main Method (cont)

• public class Lab01
• public static void main(String args)
• Lab01 lab new Lab01()
• lab.output()
• public void output()
• System.out.println(1 2 Hello World)

94
The main Method (cont)

• public class Lab01
• public static void main(String args)
• Lab01 lab new Lab01()
• lab.output()
• public void output()
• System.out.println(1 2 Hello World)

95
The main Method (cont)

• public class Lab01
• public static void main(String args)
• Lab01 lab new Lab01()
• lab.output()
• public void output()
• System.out.println(1 2 Hello World)

96
Java
Object Oriented Programming
Control Structures
97
Refers to the order in which the individual
statements of a program are executed or evaluated
Control Structures
98
Control Structures

• Sequential (Default)
• Branching
• Conditional
• Repetition (looping)

99
Sequential ControlStatements are executed in
the order in which they are written.
Control Structures
100
System.out.println(ABC)System.out.println(DEF
)
Control Structures
101
System.out.println(ABC)System.out.println(DEF
)
Control Structures
Output ABCDEF
102
BranchingAllows the flow of execution to jump
to a different part of the program.
Control Structures
103
public static void main(String args) Lab01
lab new Lab01() lab.output()public void
output() System.out.println(Hello World)
Control Structures
104
public void methodA() methodB() methodC()
public void methodB() System.out.print(Hello
)public void methodC() System.out.print(
World)
Control Structures
105
Questions?
106
Java
Object Oriented Programming
Begin Lab 01