Java程序員認(rèn)證考試
Sun Java認(rèn)證分為兩個(gè)級(jí)別：Sun 認(rèn)證Java程序員和Sun 認(rèn)證Java開(kāi)發(fā)員。下面是小編整理的關(guān)于Java程序員認(rèn)證考試，希望大家認(rèn)真閱讀!
SUN認(rèn)證
SUN認(rèn)證是給網(wǎng)絡(luò)設(shè)計(jì)界建立的一套認(rèn)證標(biāo)準(zhǔn)，Sun公司推出了Java以及Solaris技術(shù)認(rèn)證方案。對(duì)于企業(yè)而言，可以借助這項(xiàng)認(rèn)證作為招聘人才的評(píng)判標(biāo)準(zhǔn)，或是作為衡量員工技術(shù)水準(zhǔn)的依據(jù);在個(gè)人方面，通過(guò)這些認(rèn)證也可以證明個(gè)人的技術(shù)能力。
1.Java認(rèn)證考試 該認(rèn)證主要面對(duì)Java程序員。同時(shí)，該認(rèn)證是業(yè)界唯一經(jīng)Sun授權(quán)的Java認(rèn)證，考試內(nèi)容涉及所有Java相關(guān)知識(shí)、編程概念及applet開(kāi)發(fā)技巧。Sun認(rèn)證Java程序員考試旨在觀察您通過(guò)應(yīng)用軟件分配進(jìn)行復(fù)雜編程的能力，之后還要測(cè)試您完成編程所需的知識(shí)。每次考試都包括65道以上的選擇題，時(shí)間大約為90分鐘。目前在這方面有兩項(xiàng)認(rèn)證：Sun Certified Java Programmer(SCJP)和 Sun Certified Java Developer
(SCJD)。SCJP測(cè)驗(yàn)Java程序設(shè)計(jì)概念及能力，內(nèi)容偏重于Java語(yǔ)法及JDK的內(nèi)容;SCJD則進(jìn)一步測(cè)試用Java開(kāi)發(fā)應(yīng)用程序的能力，考試者必須先完成一個(gè)程序的設(shè)計(jì)方案，再回答與此方案相關(guān)的一些問(wèn)題。 2. Solaris系統(tǒng)管理認(rèn)證考試
對(duì)Solaris/Sun OS系統(tǒng)管理員，Sun推出Certified Solaris Administrator(CSA)。CSA分別為兩個(gè)等級(jí)(Part Ⅰ和 Part Ⅱ)，測(cè)試對(duì)Solaris系統(tǒng)管理的了解程度。
3. Solaris網(wǎng)絡(luò)管理認(rèn)證考試
為了測(cè)試使用者對(duì)于Solaris網(wǎng)絡(luò)管理能力，Sun推出Certified Network Administrator(CNA)。內(nèi)容包括基本網(wǎng)絡(luò)概念、Routing and Subnet、Security、Performance、DNS、NIS+等。
通過(guò)SUN任何一門專業(yè)認(rèn)證后，考生將收到SunMicrosystems總公司寄發(fā)的資格證書及徽章，并有權(quán)將通過(guò)Sun認(rèn)證的標(biāo)記印在個(gè)人名片上，作為個(gè)人技術(shù)能力的肯定。
SUN JAVA程序員認(rèn)證考試大綱
Basic Object Oriented Concept
Object
An instance of a class
Has state and behavior
State is contained in its member variables
Behavior is implemented through its methods.
Message
For objects to interact with one another
Result of a message is a method invocation which performs actions or modifies the state of the receiving object
Classes
An object`s class is the object`s type
The ability to derive one class from another and inherit its state and behavior
Most general classes appear higher in the class hierarchy
Most specific classes appear lower in the class hierarchy
Subclasses inherit state and behavior from their superclasses
Interface
A collection of method definitions without actual implementations
For defining a protocol of behavior that can be implemented by any class anywhere in the class hierarchy.
Packages
A collection of related classes and interfaces
java.lang is imported by default automatically
Java Language Fundamentals
The order for every "heading" is as follows:
package declarations -- package my.applications.uinterfaces;
import statements -- import java.awt.*
class definitions -- public class myClass { .....
Order of public vs. non-public class definitions doesn`t matter.
Allows only one top-level public class per source file
Name of source file must be the same as name of the public class
main() method must be:
public
static
Not return a value (void return type)
Take an array of strings:(String[] args) or (String args[]) doesn`t matter
`args` is just a common name, you can use any name you like. However, there must be a set of "[]"
Legal examples:
public static void main(String[] args)
static public void main(String args[])
Command line arguments are placed in the String array starting at 0 after the java command and the program name
For non-applet java application, there must be a main method
For applet, you do not use main()
Applet:
a subclass of Panel, which itself is a subclass of Container
init() - called when applet is first instantiated.
start() - called when the web page containing the applet is to be displayed
stop() - called when the web browser is about to show another web page and quit the current one
HTML required to display an applet in a web page:
PARAM tag allows you to pass a value to an applet:
To use these values in your applet, use the getParameter(String paramname ) method to return the value as a string:
greeting=getParameter("message");
Java Identifier
Consists of letters and digits
Must begin with a letter , "$" or "_"
Unlimited length
Cannot be the same as a reserved keyword
Java Reserved Word
Reserved Keywords cover categories such as primitive types, flow control statements, access modifiers, class, method, and variable declarations, special constants, and unused words
abstract - boolean - break - byte - case - catch - char - class - const - continue - default - do - double - else - extends - final - finally - float - for - goto - if - implements - import - instanceof - int - interface - long - native - new - null - package - private - protected - public - return - short - static - super - switch - synchronized - this - throw - throws - transient - try - void - volatile - while
True, false and null are literals, not keywords
Primitives
Occupy pre-defined numbers of bits
Have standard implicit initial values
Type conversion
You cannot assign booleans to any other type.
You cannot assign a byte to a char.
You can assign a variable of type X to type Y only if Y contains a wider range of values than X.
Primitives in order of `width` are char/short, int, long, float, double.
For Objects, you can assign object X to object Y only if they are of the same class, or X is a subclass of Y, which is called "upcasting".
Promotion
In arithmetic operations, variable may be widened automatically for the purpose of evaluating the expression
The variables themselves would not be changed, but for its calculations Java uses a widened value.
Casting
Similar to forcing a type conversion - values can be casted between different primitive types
Done by placing the destination cast type keyword between parentheses before the source type expression
Some cast operations may result in loss of information
Variables derived from these primitive types that are declared in nested blocks could only be accessible within that block and its sub-blocks, and are destroyed when the block they belong to is stopped
Major primitive types:
Primitive Type
Size
Range of Values
Byte
8 bit
-27 to 27-1
Short
16 bit
-215 to 215-1
Int
32 bit, all are signed
-231 to 231-1
Long
64 bit
-263 to 2 63-1
Char
16 bit unicode
`/u0000` to `/uffff`
(0 to 216-1 )
Java unicode escape format: a "/u" followed by four hexadecimal digits. e.g.,
char x=`/u1234`
Other primitive types:
Long - can be denoted by a trailing "l" or "L"
Float - can be denoted by a trailing "f" or "F"
Double - can be denoted by a trailing "d" or "D"
Booleans - true or false only, cannot be cast to or from other types
Array - declared using the square brackets "[]". Example of legal declarations :
int[] x;
int x[];
int i[][]; declares a two dimensional array.
Can be created dynamically using the new keyword
Can be created statically using an explicit element list
Array element counts from 0. For example, int[10] actually has 10 elements, from 0 to 9, not from 1 to 10
Array can be constructed after declaration, or to have everything done on the single line
int[] i;
i = new int[10];
OR
int i[] = new int[10];
Array members can be initialized either through a FOR loop, or through direct assignment
int myarray[] = new int[10];
for(int j=0; j
myarray[j]=j;
}
OR
char mychar[]= new char[] {`a`,`e`,`i`,`o`,`u`};
Do not get confused with string. Strings are implemented using the String and StringBuffer classes.
Bitwise Operation
numerics can be manipulated at the bit level using the shift and bitwise operators
Java includes two separate shift-right operators for signed and unsigned operations, the ">>" and the ">>>"
>> performs a signed right-shift. If the first bit on the left is 1, then when it right-shifts the bits, it fills in a 1s on the left. If the leftmost bit is 0, then when it right-shifts the bits, it fills in a 0s on the left. The first bit represents the sign of a number to preserve the sign of the number.
>>> performs an unsigned right-shift. The left side is always filled with 0s.
<< performs a left-shift. The right side is always filled with 0s.
Java Operator
Operators that compare values
equal to, "=="
not equal to, "!="
greater than, ">"
less than, "<"
greater than or equal to, ">="
less than or equal to, "<="
Logical Operators
logical AND, "&"
logical OR, "|"
logical XOR, "^"
boolean NOT, "!"
short-circuit logical AND, "&&"
short-circuit logical OR, "||"
Operator precedence determines the order of evaluation when different operators are used, although precedence can be explicitly set with parentheses "()".
Multiple operators of the same precedence are evaluated from left to right
In logical boolean expressions, the right operand is only evaluated after the left hand operand has been evaluated first.
For short-circuit logical expression, if the left hand condition does not evaluate to true, the right hand condition will not be evaluated at all
For Objects, == determines whether the variables reference the same object in memory, rather than comparing their contents.
For example, when
String x = "Hey";
String y = "Hey";
Java creates only one String object, so the result of comparison is always true.
To avoid the above situation, use the NEW keyword so that string x and y can be of different objects.
In Booleans, equals() returns true if the two objects contain the same Boolean value.
In String, equals() returns true if the Strings contain the same sequence of characters.
Java Modifiers
private
Accessible only from inside the class
Cannot be inherited by subclasses
protected
Accessible only by classes in the same package or subclasses of this class
public
Can be accessed by anyone
static
Belongs to the class, not to any particular instance of the class
For variables, there is only one copy for all instances of the class. If an instance changes the value, the other instances see that changes
For methods, it can be called without having created an instance, and cannot be used the this keyword, nor be referred to instance variables and methods directly without creating an instance For inner classes, they can be instantiated without having an instance of the enclosing class
Methods of the inner class cannot refer to instance variables or methods of the enclosing class directly
final
Variable`s value cannot be changed
Methods cannot be overridden
Classes cannot be subclassed.
native
Method written in non java language
Outside the JVM in a library
Optimized for speed
abstract
Method which is not implemented with code body
synchronized
method makes non-atomic modifications to the class or instance
for static method, lock for the class is acquired before executing the method
for non-static method, a lock for the specific object instance is acquired
transient
field is not part of the object`s persistent state
should not be serialized
volatile
field may be accessed by unsynchronized threads
certain code optimizations must not be performed on it
none
class- non-public class is accessible only in its package
interface - non-public interface is accessible only in its package
member - member that is not private, protected, or public is accessible only within its package
Summary of Class Member Accessibility
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