JavaAdvanced programming for expertes dsd

JavaAdvanced programming for expertes dsd

• 1.
  Advanced Java Programming CS537 – Data Structures and Algorithms
• 2.
  The Stack • Thestack is the place where all local variables are stored – a local variable is declared in some scope – Example int x; // creates the variable x on the stack • As soon as the scope ends, all local variables declared in that scope end – the variable name and its space are gone – this happens implicitly – the user has no control over it
• 3.
  The Heap • Theheap is an area of memory that the user handles explicitly – user requests memory through new operator – java does garbage collection to reclaim unused memory • A user maintains a handle on memory allocated in the heap with a reference variable
• 4.
  Creating Objects • Allobjects are created on the heap • A reference to object is stored on the stack – simply declaring an object does not create it • automatically set to null – new operator allocates space on the heap
• 5.
  Creating Objects • Example Objectobj1 = new Object(); Object obj2; main x = 3 func1 obj1 = 200 obj2 = null 200 Heap Stack Object
• 6.
  Assigning Object References •Reference can be assigned through new operator • obj2 = new Object(); • Reference can assigned to another reference • obj2 = obj1; • WARNING – when assigning to another reference, both references now refer to the same object
• 7.
  Assigning Object References •Example • Object obj1 = new Object(); • Object obj2 = obj1; main x = 3 func1 obj1 = 200 obj2 = 200 200 Heap Stack Object
• 8.
  Simple Class class Fooimplements Cloneable { private int num; public void Foo(int num) { this.num = num; } public void setNum(int num) { this.num = num; } public int getNum() { return num; } }
• 9.
  Copying an Object •Want to create and modify copy of object – remember, simple assignment not enough Foo f1 = new Foo(5); Foo f2 = f1; // still only one object – 2 references f2.setNum(10); System.out.println(“f1’s num = “ + f1.getNum()); // prints 10 System.out.println(“f2’s num = “ + f2.getNum()); // prints 10 – need to use the clone() method
• 10.
  clone() Method • Touse clone() must implement Cloneable • Object.clone() is automatically inherited by every class – by default, it creates a new object and copies all fields • Example Foo f1 = new Foo(5); Foo f2 = f1.clone(); f2.setNum(10); System.out.println(“f1’s num = “ + f1.getNum()); // prints 5 System.out.println(“f2’s num = “ + f2.getNum()); // prints 10
• 11.
  Shallow Clone • Onlycopies the fields – does not copy what the fields reference • Doesn’t work well for sophisticated objects • Example: Class Foo { private int [] nums; public void Foo(int size) { nums = new int[size]; } … } Foo f1 = new Foo(5); Foo f2 = f1.clone();
• 12.
  Shallow Clone Foo f1= new Foo(5); Foo f2 = f1.clone(); func1 f1 = 200 f2 = 100 200 Heap Stack nums = 50 50 Array nums = 50 100
• 13.
  Deep Clone • Copiesfields and what they refer to • Must reimplement the clone() method class Foo { … public Object clone() { try { Foo fobj = (Foo)super.clone(); // copies fields fobj.nums = (int)nums.clone(); // arrays implement clone return fobj; } catch(CloneNotSupportedException e) { } } }
• 14.
  Inheritance • lets oneclass inherit fields and methods from another class • use keyword extends to explicitly inherit another classes public and protected fields/methods • can only explicitly extend from one class • all classes implicitly extend the Object class
• 15.
  Inheritance • overriding amethod – must have the same signature as original – declaring a method final means future derived classes cannot override the method • overloading a method – method has same name but different signature – they are actually different methods
• 16.
  Inheritance • abstract classesand methods – declaring a class abstract • must have an abstract method • class cannot be directly used to create an object • class must be inherited to be used – declaring a method abstract • method must be defined in derived class
• 17.
  Abstract Class abstract classPixel { . . . public abstract void refresh(); } class ColorPixel extends Pixel { . . . public void refresh() { do some work } } • Note: signature of method in derived class must be identical to parent declaration of the method
• 18.
  Interface • basically anabstract class where all methods are abstract • cannot use an interface to create an object • class that uses an interface must implement all of the interfaces methods • use the implements keyword • a class can implement more than one interface
• 19.
  Interface • simple example classTester implements Foo, Bar { . . . } • Foo and Bar are interfaces • Tester must define all methods declared in Foo and Bar
• 20.
  Array Review • Consecutiveblocks of memory • Creation: int [] grades = new int[25]; • __.length: holds size of array • __.clone(): makes copy of array data • out-of-bounds exception: trying to access data outside of array bounds generates an exception • Array size is fixed at creation
• 21.
  Vector Class • Verysimilar to an array • Major difference: vectors can grow beyond original size – if a certain capacity is exceeded, a new, larger memory region is allocated for vector – copy all data to the new area • See Java documentation on-line for complete details