Lecture 21b
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8 Classes and Objects: A Deeper Look 2005 Pearson Education, Inc. All rights reserved.
2
OBJECTIVES In this chapter you will learn: Encapsulation and data hiding. The notions of data abstraction and abstract data types (ADTs). To use keyword this. To use static variables and methods. To import static members of a class. To use the enum type to create sets of constants with unique identifiers. How to declare enum constants with parameters.
2005 Pearson Education, Inc. All rights reserved.
3
8.2 Time Class Case Study •public services (or public interface) – public methods available for a client to use
• If a class does not define a constructor the compiler will provide a default constructor • Instance variables – Can be initialized when they are declared or in a constructor – Should maintain consistent (valid) values
IT114
Winter 2007
R.B. Lenin
DA-IICT
2005 Pearson Education, Inc. All rights reserved.
4
IT114
Winter 2007
R.B. Lenin
DA-IICT
2005 Pearson Education, Inc. All rights reserved.
5
8.2 Time Class Case Study (Cont.) •String method format – Similar to printf except it returns a formatted string instead of displaying it in a command window
•new implicitly invokes Time1’s default constructor since Time1 does not declare any constructors
IT114
Winter 2007
R.B. Lenin
DA-IICT
2005 Pearson Education, Inc. All rights reserved.
6
IT114
Winter 2007
R.B. Lenin
DA-IICT
2005 Pearson Education, Inc. All rights reserved.
7
IT114
Winter 2007
R.B. Lenin
DA-IICT
2005 Pearson Education, Inc. All rights reserved.
8
IT114
Winter 2007
R.B. Lenin
DA-IICT
2005 Pearson Education, Inc. All rights reserved.
8.4 Referring to the Current Object’s Members with the this Reference
9
• The this reference – Non-static methods implicitly use this when referring to the object’s instance variables and other methods – Can be used to access instance variables when they are shadowed by local variables or method parameters
• A .java file can contain more than one class – But only one class in each .java file can be public
IT114
Winter 2007
R.B. Lenin
DA-IICT
2005 Pearson Education, Inc. All rights reserved.
10
IT114
Winter 2007
R.B. Lenin
DA-IICT
2005 Pearson Education, Inc. All rights reserved.
11
IT114
Winter 2007
R.B. Lenin
DA-IICT
2005 Pearson Education, Inc. All rights reserved.
8 Classes and Objects: A Deeper Look 2005 Pearson Education, Inc. All rights reserved.
2
OBJECTIVES In this chapter you will learn: Encapsulation and data hiding. The notions of data abstraction and abstract data types (ADTs). To use keyword this. To use static variables and methods. To import static members of a class. To use the enum type to create sets of constants with unique identifiers. How to declare enum constants with parameters.
2005 Pearson Education, Inc. All rights reserved.
3
8.2 Time Class Case Study •public services (or public interface) – public methods available for a client to use
• If a class does not define a constructor the compiler will provide a default constructor • Instance variables – Can be initialized when they are declared or in a constructor – Should maintain consistent (valid) values
IT114
Winter 2007
R.B. Lenin
DA-IICT
2005 Pearson Education, Inc. All rights reserved.
4
IT114
Winter 2007
R.B. Lenin
DA-IICT
2005 Pearson Education, Inc. All rights reserved.
5
8.2 Time Class Case Study (Cont.) •String method format – Similar to printf except it returns a formatted string instead of displaying it in a command window
•new implicitly invokes Time1’s default constructor since Time1 does not declare any constructors
IT114
Winter 2007
R.B. Lenin
DA-IICT
2005 Pearson Education, Inc. All rights reserved.
6
IT114
Winter 2007
R.B. Lenin
DA-IICT
2005 Pearson Education, Inc. All rights reserved.
7
IT114
Winter 2007
R.B. Lenin
DA-IICT
2005 Pearson Education, Inc. All rights reserved.
8
IT114
Winter 2007
R.B. Lenin
DA-IICT
2005 Pearson Education, Inc. All rights reserved.
8.4 Referring to the Current Object’s Members with the this Reference
9
• The this reference – Non-static methods implicitly use this when referring to the object’s instance variables and other methods – Can be used to access instance variables when they are shadowed by local variables or method parameters
• A .java file can contain more than one class – But only one class in each .java file can be public
IT114
Winter 2007
R.B. Lenin
DA-IICT
2005 Pearson Education, Inc. All rights reserved.
10
IT114
Winter 2007
R.B. Lenin
DA-IICT
2005 Pearson Education, Inc. All rights reserved.
11
IT114
Winter 2007
R.B. Lenin
DA-IICT
2005 Pearson Education, Inc. All rights reserved.
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