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Object Oriented Software Development
Object Oriented Software Development
Object Oriented Software Development Naufal F. Setiawan School of - - PowerPoint PPT Presentation
Object Oriented Software Development Naufal F. Setiawan School of - - PowerPoint PPT Presentation
Object Oriented Software Development Object Oriented Software Development Naufal F. Setiawan School of Computing and Information Systems University of Melbourne Workshop 2 (All images from Wikimedia Commons) Object Oriented Software
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Object Oriented Software Development
Question 1 cont...
Why shouldn’t we use == on Strings or other objects (i.e. Classes that we may make later)? Answer
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Object Oriented Software Development
Question 1 cont...
spidey1 spidey2 Implementation spidey1 == spidey2 will return false. spidey1.equals(spidey2) should return true. spidey1 == spidey1 will return true.
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Object Oriented Software Development
References
In Java, non-primitive variables are stored using references. References are similar to pointers in the sense that they store addresses to where instances are stored. They are much nicer than pointers as we don’t need manual dereferencing (&, *, ->). We may find it useful to visualize references as name tags.
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Object Oriented Software Development
Visualizing Variables
Code new Elephant();
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Object Oriented Software Development
Visualizing Variables
elph1 Code Elephant elph1 = new Elephant();
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Object Oriented Software Development
Visualizing Variables
elph1 elph2 Code Elephant elph2 = elph1;
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Object Oriented Software Development
Visualizing Variables: Mutations
elph1 elph2 Code // does elph2 change too? elph1.setFace(new HumanFace());
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Object Oriented Software Development
Visualizing Variables: Mutation = Reassignment!
elph1 elph2 Code elph2 = new Elephant();
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Object Oriented Software Development
Visualizing Variables
Recap: var = ... Assignment is like slapping name tags. On other contexts, the variable refers to whatever it is referring/pointing to.
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Object Oriented Software Development
Question 2
What is method overloading? Answer
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Object Oriented Software Development
Overloading Examples
The Good public void connect(String url) {} public void connect(IPAddress ip) {} The Bad public float max(float x, double y) { ... } public float max(double x, float y) { ... }
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Object Oriented Software Development
Java Theory
What is type casting, and describe the following types of type casting: Answer Type casting: Explicit typecasting: Implicit typecasting:
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Object Oriented Software Development
Java Theory
What is boxing and unboxing? Answer Boxing: a typecast Unboxing: a typecast
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Object Oriented Software Development
Boxing Example
Boxed variables are stored as an object, while unboxed variables are stored as a primitive data. Example int someNumber = 3; Integer boxedNumber = 3; someNumber.shortValue(); // doesn't work boxedNumber.shortValue(); // works Boxing does not have many benefits for now until we learn Generics later on.
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Object Oriented Software Development
Wrapper Classes are still useful
Most wrapper classes are useful due to their static methods. Example int number = Integer.parseInt(inputString); Notice that the most visible difference between a static and instance method is how we call them!
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Object Oriented Software Development