Computing Concepts with Java Essentials

1
Computing ConceptswithJava Essentials

• Chapters1, 2 3

2
Page 23 Escape Sequences

• To display a String
• System.out.println(String)
• For example
• System.out.println(Hello Karel)
• generates the output Hello Karel

3
Page 23 Escape Sequences

• How is the String Hello Karel generated
• to display double quotes precede the with a
  backslash, i.e. \ is used to display a single
  double quote ().
• System.out.println(Hello \Karel\)

4
Page 23 Escape Sequences

• Other common escape sequences
• System.out.println(\\) outputs \
• System.out.println(\n) outputs endOfLine
• System.out.println(\u00E9) outputs the
  corresponding unicode character(é).

5
Page 42 Defining A Class

• A class defines the methods that you can apply to
  its objects

6
Page 42 Defining A Class

• A method definition contains the following parts
• An access specified (usually private)
• The return type of the method (void, int, )
• The name of the method
• A list of the parameters of the method, enclosed
  in parentheses
• The body of the method

7
Page 47 Instance Fields

• A object stores its state in one or more instance
  fields
• An instance field declaration consists of the
  following parts
• An access specifier (usually private)
• The type of the variable (String, int, Robot, .)
• The name of the variable
• A possible initialization (well discuss default
  initialization values)

8
Page 49/50 Constructors

• A constructor specifies how an object should be
  initialized
• A constructor has the same name as the class

9
Page 50 Constructors

• Constructors are generally declared as public
• The new operator invokes the constructor
• Constructors do not have return types

10
Page 62 Common Error

• A constructor is invoked only when an object is
  first created
• The constructor can not be called to reset an
  object

11
Chapter 3, Section 1 Number Types

• The int type denotes integers without fractional
  parts
• The double type denotes floating point numbers.

12
Chapter 3, Section 1 Number Types

• Why separate int and double types.
• int(egers) are more efficient
• less storage
• process faster
• no rounding errors

13
Chapter 3, Section 1 Number Types

• Numeric Ranges
• -2,147,483,648 lt int lt 2,147,483,647
• Integer.MIN_VALUE lt int lt Integer.MAX_VALUE
• double (Floating points) store about 15
  significant digits

14
Chapter 3, Section 1 Other Types
The eight primitives are

• Numeric Types
• byte
• short
• int
• long
• float
• double

• Other
• boolean
• char

Types on AP exam
15
Chapter 3, Section 3 Combining Assignment
Arithmetic

• -
• /

16
Chapter 3, Section 3 Constants

• Constants are defined with the keyword final
• The form of a constant variable declaration is
• accessSpecifier final type variableName value
• The variable Name should be in ALL caps!
• Ex.private final double MIN_GPA 3.2

17
Chapter 3Common Error 3.1

• Integer Division
• 15 / 4
• 15 / 4.
• 15. / 4
• 12 3 / 4
• 12 3 / 4.
• 12. / ( 7 / 8)

18
Round-off Error Why?

• double f 4.35
• int n (int) (100 f)
• System.out.println(n)
• 434 prints Why?
• Remember ICT? Write out ¾ in binary. No problem.
  Now, try to write out 23/47 in binary.

19
Chapter 3, Section 5 Static Methods

• A static method does not operate on an object
• Static method call
• ClassName.methodName(parameters)
• Example
• Math.sqrt(4)
• Point2d.distance(x1, y1, x2, y2)

20
Chapter 3, Section 6 Type Conversion

• Assignments require that both types be compatible
• In Java, assigning a double to an int(narrowing)
  is an error but assigning an int to a double
  is ok(widening)
• In Java, one type can be cast to another type
• Cast Syntax
• int x (int) 4.3 // hey, compiler. I know more
  than you, so Im going to override what you
  normally do. If Im wrong, an error will occur at
  run-time. (essentially, thats casting)

21
Chapter 3, Section 6 Type Conversion

• Example of casting a double to int
• int numBeepers (int) (4.5)
• double price 13.6
• int dollar (int) price
• dollar (int) price 0.5
• dollar (int) (price 0.5)
• dollar Math.round(price)
• price has not been changed!

22
Chapter 3, Advance Topic 3.4Binary Number

• Remember ICT, its back
• Binary numbers digits from the set 0,1
• Conversion
• binary ? hexadecimal
• binary ? decimal
• hexadecimal ? decimal

23
Chapter 3, Section 7 String

• A string is a sequence of characters
• If one argument of the operator is a string,
  the other argument is converted to a string
• If a string contains the digits of a number, the
  Integer.parseInt or Double.parseInt methods
  return the numeric value
• int num Integer.parseInt(245)

24
Chapter 3, Section 7 String

• The substring method extracts a part of the
  string
• String positions are counted starting with 0.
• .substring(beginIndex, endIndex) -or-
• .substring(beginIndex)
• String str1 Hi There.substring(1,3)
• String str2 Hi There.substring(3)

25
Chapter 3, Section 8 Reading Input

• What do we want to put here?????

26
Chapter 3, Section 10Comparing Primitives and
Objects

• Primitive type variables hold values
• Object variables hold references
• The difference
• When a primitive type is copied, the original and
  copy are independent values
• When you copy a reference, both variable
  reference the same object (aliasing)

27
Comparing Objects

• .equals() // for all classes
• if ( str1.equals(str2)
• .compareTo() // for classes implementing
  Comparable
• if ( str1.compareTo(str2) gt 0 )
• //str1 is greater than str2
• else if ( str1.compareTo(str2) lt 0 )
• // str1 is less than str2
• else if ( str1.compareTo(str2) 0 )
• // they are equal