java 编程笔记.docx
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java 编程笔记.docx
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java编程笔记
JavaNotesfor“ProgrammingLanguages”and
“AdvancedProgramming”
CourseURLs:
http:
//www.cs.biu.ac.il/~hasonz
http:
//www.cs.biu.ac.il/~akivan/APCourse.html
oldCourseURLs:
http:
//www.cs.biu.ac.il/~luryar
http:
//www.cs.biu.ac.il/~linraz
//FrstProg.javafile
classFrstProg
{
/*Thisprogramjustwritessomethingtotheconsole
andwillstopexecuting*/
publicstaticvoidmain(String[]args)
{
System.out.println("Thisisthefirstlesson");
//printlnispartofAPI
}
}
HOWTOCOMPILEANDRUNJAVAFILES:
JavaCompiler:
javacFrstProg.java(createsFrstProg.class)
JavaInterpreter:
javaFrstProg(executesFrstProg.class)
Output:
Thisisthefirstlesson
-Comments//…or/*…*/or/**…*/
-Blocks{…}
-Methods
-mainmethod(alwayspublicstaticvoid)
-Identifiers(UpperCase,LowerCase,_,$,Digits)cannotstartwithdigit
casesensitive(TOTAL,Total,total)
-Consistencyinnaming(BeginningLowercase=>methodsandidentifiers
BeginningUppercase=>classes
AllUppercase=>constants
-printandprintlnmethods
-commandlinearguments(mainmethod)
-objectorientedprogramming(classes,objects,inheritance,etc.)
//Turkey.javaFile
classTurkey
{
publicstaticvoidmain(String[]args)
{
System.out.print("Theinternational"
+"dialingcode");
System.out.print("forTurkeyis"+90);
}
}
//NameTag.javaFile
classNameTag
{
publicstaticvoidmain(String[]args)
{
System.out.println("Hello!
Mynameis"+args[0]);
}
}
javacNameTag.java(compile)
javaNameTagXXX(run)
Hello!
MynameisXXX(output)
Toimportapackage:
importpackage.class;
Or:
importpackage.*;
JAVAAPI(ApplicationProgrammingInterface)
View:
Download:
Packages
java.appletcreatesprograms(applets)thatareeasilytransportedacross
theweb.
java.awt(AbstractWindowingToolkit)Drawgraphicsandcreate
graphicaluserinterfaces.
java.ioperformawidevarietyofI/Ofunctions.
java.langgeneralsupport.Itisautomaticallyimported.
java.mathforhighprecisioncalculations.
communicateacrossanetwork.
java.rmi(RemoteMethodInvocation)createprogramsthatcanbe
distributedacrossmultiplecomputers.
java.sqlinteractwithdatabases.
java.textformattextforoutput.
java.utilgeneralutilities.
PRIMITIVEDATATYPES:
byte8bits-128127
short16bits-3276832767
int32bits-2billion2billion
long64bits-10191019
Floatingpoint:
float32bits
double64bits
Others:
char16bits65536Unicodecharacters
booleanfalsetrue
void
WRAPPERCLASSES:
Classesdeclaredinpackagejava.lang:
ByteFloatCharacterBooleanVoid
ShortDouble
Integer
Long
OPERATORS:
Unary:
+-
Binary:
*/%Multiplication,division,remainder
+-Addition,subtraction
+Stringconcatenation
=Assignment
+=-=*=/=%=
count++returncountandthenadd1
++countadd1andthenreturncount
count--returncountandthensubtract1
--countsubtract1andthenreturncount
!
Logicalnot^Bitwisexor==!
=
&&Logicaland&Bitwiseand><
||Logicalor|Bitwiseor>=<=
CODITIONSANDLOOPS:
condition?
expression1:
expression2
example:
intlarger=(num1>num2)?
num1:
num2;
if(condition)switch(expression){
Statement1casevalue1:
elseStatement-list1;break;
Statement2casevalue2:
Statement-list2;break;
….
default:
Statement-list3;
}
while(condition)doStatementfor(init;cond;incr)
Statement;while(condition);Statement;
continuebreakreturn
INSTANTIATIONANDREFERENCES
classCarExample
{
publicstaticvoidmain(String[]args)
{
inttotal=25;
intaverage;
average=20;
//CarClassshouldbedeclared
CarClassmyCar=newCarClass();
CarClassyourCar;
yourCar=newCarClass();
//Tocallamethoduse"."
myCar.speed(50);
yourCar.speed(80);
System.out.println("Mycarcost$"+myCar.cost());
}
}
classCarClass
{
int_speed;
int_cost;
CarClass()
{
_speed=0;
_cost=2500;
}
publicvoidspeed(intspeed)
{
_speed=speed;
}
publicintcost()
{
return_cost;
}
}
GARBAGECOLLECTION
Objectsaredeletedwhentherearenomorereferencestothem.Thereisapossibility
tohavetheSystemrunthegarbagecollectorupondemandusingtheSystem.gc()
method.
Callingthegc()methodsuggeststhattheJavaVirtualMachineexpendefforttoward
recyclingunusedobjectsinordertomakethememorytheycurrentlyoccupyavailable
forquickreuse.Whencontrolreturnsfromthemethodcall,theJavaVirtualMachine
hasmadeabestefforttoreclaimspacefromalldiscardedobjects.
Ifweaddtheline:
CarClassmomCar=myCar;
wegetthefollowingdrawing:
Toreducethenumberofreferencestoanobject,
W
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