Java Daily issues Summary-01

1.Java source file suffix name (not compiled file) is. Java, Javac.exe compiled as a binary file. Class is compiled as an. exe executable file by Java.exe

2.%, priority with */, left-to-right

3.final-Modified classes cannot be inherited

Final modified methods cannot be overridden by a quilt class

Final modified variable cannot change assignment

The final modified reference type cannot be modified to point to, but can change the contents of the inside

The difference between 4.& and &&

if (a++>2&b++>2) to determine the former is false, continue to judge, if (A++>2&&B++>2) The former is false do not continue to judge the direct output false

5.Collection

List (ordered)

ArrayList (differs from LinkedList in that it is more suitable for random access) capacity capacity auto-growth

LinkedList (more suitable for inserting and deleting) doubly linked list

Vector (synchronization is more secure, but performance is almost)

Stack (push stack pop out peek gets stack top element empty determines empty search query for an element position)

Set (unordered)

Map

HashMap: Allow non-null, non-synchronous

Hashtable: Implements the Map Interface hash table, Key-value,put (,) puts the data get (,) takes the data; not null; synchronous

Multiple threads operate on a class, take advantage of synchronization, and synchronize thread safety

6.try{}catch{}finally{}

The finally block executes regardless of whether there is an exception in the try;

Finally statement block executes before the CATCH statement block return

The TRY statement block and the catch statement block if there is a system.exit (0) to end the program immediately

Return in a finally statement block overrides the return value of the TRY statement block

7. Class variables or instance variables are not empty until they are used, but local variables must be assigned values

8.primitive types Basic Data type

Each basic data type in Java corresponds to a reference data type Int-integer float-float

9.jar combine many classes into one jar file

Javac the source file. Java is compiled into binary files. class

Javadoc extracting comments from a source file for classes, methods, and members forms an API help document supporting the source code

10. Dependency Injection IOC container reduces coupling between components, making development more concise

The 11.try{}catch{},try statement block can be followed by multiple catch statement blocks, which, in turn, match the exception object that is thrown by the try statement block and the exception type declared by the catch statement block, and the catch statement block is executed if the exception object is consistent with the exception type or its subclasses

The back is not going to be executed

Virtual classes in 12.c++ are the same as abstract classes in Java

A subclass can inherit multiple abstract classes, but it can implement multiple interfaces

Abstract classes are not necessarily abstract methods, but can also be method bodies, but the interfaces must be abstract classes

13. The method does not inherit one saying that only overrides and overloads

Java Daily issues Summary-01