02章

2.Where storage lives
s
Register Stack
STACK
i (5)
Heap
Constant storage
HEAP
“ABC”
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3.Special case: primitive types
Primitive type Size Minimum Maximum Wrapper type
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11.Concurrent programming
A common example of concurrency is the user interface. By using tasks, a user can press a button and get a quick response rather than being forced to wait until the program finishes its current task.
2.You must create all the objects
String s; // s.length() ?? String s =new String(“ABC”); // String s =“ABC”;
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CODE
String s=new String(“ABC”);
int i=5;
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1.Manipulate objects with references
HTML Java does not support pointer (Syntax) But implemented by pointer (perhaps) String s; // Reference only String s = "asdf"; // Instance Example: •Television / remote control •File / file handle
The garbage collector “knows” when an object is no longer in use, and it then automatically releases the memory for that object.
11.Exception handling
An exception is an object that is “thrown” from the site of the error and can be “caught” by an appropriate exception handler designed to handle that particular type of error.
char ch=„x‟; Character c= new Character(„x‟);
Autoboxing
Character ch = „x‟; char c = ch;
BigDecimal & BigInteger
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4.Arrays in Java
Objects (not pointers) Auto boundary checking •C/C++ memory overflow Creation •int[ ] aint=new int[5];
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Default values for primitive members Primitive type Default
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5.Reusing the implementation
Composing a new class from existing classes, this concept is called composition.
Composition is often referred to as a “has-a” relationship, as in “A car has an engine.”
String[] arr = new String[10]; arr.length; arr[0].length(); //?
•Array of objects
creating an array of references Its elements are initialized to null
boolean char byte short int long
— 16-bit 8-bit 16-bit 32-bit 64-bit
— Unicode 0 -128 -215 -231 -263ห้องสมุดไป่ตู้
— Unicode 2 - 1 127 +2 —1 +2 —1 +2 —1
63 31 15 16
Boolean Character Byte Short Integer Long
4.The hidden implementation
Java uses three explicit keywords to set the boundaries in a class: public, private, and protected. These access specifiers determine who can use the definitions that follow.
Java uses dynamic memory allocation, exclusively. Every time you want to create an object, you use the new operator to build a dynamic instance of that object.
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6.Inheritance
add new methods overriding
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6.Inheritance
Is-a vs. is-like-a relationships
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7. Polymorphism
Casting to a base type is moving up the inheritance diagram: “upcasting.”
(using new, as seen earlier) in a special method
called a constructor.

If it is a primitive type, you can initialize it directly by assigning a value.
12.Java and the Internet
HTML JavaScript. .NET and C# J2EE:JDBC/Socket SSH:struts+spring+hibernate
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2.2 Everything is an Object
“If we spoke a different language, we would perceive a somewhat different world.” Ludwig Wittgenstein (1889-1951)
Although it is based on C++, Java is more of a “pure” object-oriented language.
C++ is hybrid because it has to support backward compatibility with the C language
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8.The singly rooted hierarchy
The name of this ultimate base class is simply Object.
9.Containers
Parameterized types (generics)
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10.Object creation & lifetime
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6.Creating new data types: class
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6.Creating new data types: class

When you define a class, you can put two types of elements in your class:
fields (sometimes called data members /
Beginning of scope
End of scope
Reference has gone “out of scope”, but the object itself still exists. Who is responsible for releasing memory: garbage collector
properties), methods (sometimes called member functions).

If the field is a reference to an object, you must initialize that reference to connect it to an actual object
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Class, Object, Message
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2.An object has an interface
Light lt = new Light(); lt.on();
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3.An object provides services
While you‟re trying to develop or understand a program design, one of the best ways to think about objects is as “service providers.” Your program itself will provide services to the user, and it will accomplish this by using the services offered by other objects.