Summary of exceptions and packages during java development

This article mainly introduces exceptions and packages in the basics of java. Friends in need can refer to it

1 Exceptions

Exception system

• Throwable

Error

# Usually major problems occur, such as: the running class does not exist or memory overflows, etc.

Do not write code to handle it

Exception

Occurs at runtime In this case, you can use try catch finally

The subclass names of Exception and Error are suffixed with the parent class name.

1.1 Methods in Throwable

##1.2 throws and throw

1.3 Exception handling

try
{
需要检测的代码；
}
catch(异常类
变量)
{
异常处理代码；
}
finally
{
一定会执行的代码；
}

Finally code block will not be executed in only one case. It was System.exit(0) that was executed before.

1.4 Custom exception

Custom class

Inherit Exception or its subclasses.

Define exception information through

constructor .

Example:

Class DemoException extends Exception
{
　　DemoException(String message)
　　{
　　　　super(message);
　　}
}

Throw a custom exception through throw.

1.5 Exception details

##2 Package

Category management of class files.

Provide multiple layers of

namespaces

to classes.
is written on the first line of the program file.

The full name of the class name is package name.class name.

Package is also a form of encapsulation.

2.1 Access between packages

The class permissions in the accessed package must be public.

Member permissions in a class: public or protected

protected is a permission provided to subclasses in other packages

Routine

2.2 Four types of permissions

##3 import

4 Jar package

4.1 Operation of Jar package

Through jar. The operation of jar by exe tool.

Create jar package

jar -cvf mypack.jar packa packb

View jar package

jar -tvf mypack.jar [>Directed file]

Decompression

jar -xvf mypack.jar

Manifest file of custom jar package

jar –cvfm mypack.jar mf.txt packa packb

【Related recommendations】

1.

Java Free Video Tutorial

2. YMP Online Manual

3. Comprehensive analysis of Java annotations

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