2023学年完整公开课版accessleveltoClass

AccessleveltoclassJavasupporttwoaccesslevelforclasses:public,andifleftunspecifiedpackage.Publicclasscanbeaccessedinanypackage.Nonpublicclasscanbeaccessedonlywithinthatpackage.TheaccessleveloftheclassClassAispublic!ClassBisnotpublic!ClassCisdifferentfromClassA/B.ClassacanbeaccessedinsideclassC,butclassBcannotbeaccessed.AccessleveltomemberspublicMembervariablesandmethodscanbeaccessedinanyclassprotectedInheritablefrompackage+subclassPackage(packagewithoutmodifier)MembervariablesandmethodscanbeaccessedbyclassesinthesamepackageprivateMembervariablesandmethodscanonlybeaccessedintheirownclassesMember'saccesslevelMembersofanyaccesslevelareintheirownclasses.Theinteriorisalwaysaccessible.ClassBandclassAarethesamepackageandcanbeaccessedinsideclassBpublic,protected,packageofclassAMembersofthelevelPrivatelevelmemberscanonlybeintheirownlocationClassisaccessed.Member'saccesslevelMembersofanyaccesslevelareintheirownclasses.TheinteriorisalwaysaccessibleClassCandclassaheterogeneouspackagescanonlybeaccessedinsideclassCpubliclevelmembersofclassAMember'saccesslevelMembersofanyaccesslevelareintheirownclasses.TheinteriorisalwaysaccessibleClassDisasubclassofclassA.ClassDcanaccesstheasheinheritedClass,distinguishingbetweenlines13and16PrivateConstructorpublic

class

Test

{

private

Test

(){}

…

}Canthisclasscreateobjects?Ifyouwanttoaddmethodstothisclass,youshouldAddinstancemethodorstaticmethod?SingletonpatternsingletonpatternpublicclassSingleton{ privatestaticSingletoninstance=newSingleton();

Privatesingleton(){}//constructorprivate publicstaticSingletongetInstance(){ returninstance; }}

publicclassTestSingleton{ publicstaticvoidmain(String[]args){ Singletons1=Singleton.getInstance(); Singletons2=Singleton.getInstance(); System.out.print(s1==s2);//true }}SingletonpatternsingletonpatternpublicclassSingleton{ privatestaticSingletoninstance;

Privatesingleton(){}//constructorprivate publicstaticSingletongetInstance(){ if(instance==null){ instance=newSingleton(); } returninstance; }}

publicclassTestSingleton{ publicstaticvoidmain(String[]args)