2.28 (defect filling) data type conversion exception handling part multi threading

Type conversion ：

1. The string type is converted to a concrete basic type

The string type is converted to a concrete basic type Convert through the method of the wrapper class corresponding to the data type

Integer： Wrapper class 、 Packaging

int Basic data type -------- object type （ Reference type ）：Integer

2. Convert basic data type to string type

summary ：

Basic data type Conversion between basic data types ：

..................byte-short-int-long-float-double

Reference type conversion ：

Subclass to parent Direct conversion

Parent class to child class     Coercive transformation   Could cause an exception (instanceof  Operator judgment ）

  exception handling ：

throws: Declaration exception   Must be used in the method ; Indicates that there may be an exception    （ Could happen , It may not happen ）

throw:throw Throw an exception explicitly It's in the body of the method Once thrown , It means that the process interrupts from the throw point , The rest of the code does not execute

A method that declares an exception is called , This calling method requires try...catch Or declare an exception

 

The superclass constructor declared an exception , Subclass constructors must declare exceptions （ Greater than or equal to parent class ）

 

 

Method rewrite , Subclasses override methods of the parent class , And subclasses declare exceptions , Then the parent class must declare an exception （ Greater than or equal to subclasses ）

 

All access modifiers in an interface cannot be private：

  The properties in the interface are constants

 

final Modify properties Constant.

final decorator , Always class （ Cut off children and grandchildren ） All methods in the representation class have final modification

 final Modification methods

Do not want to be overridden by subclasses , Business rules are absolutely consistent

final Modified class , Can't be inherited ;  final The method of decoration , Can't be rewritten ;

 

Multithreading ：

 

 

 

There are two threads to print odd and even numbers respectively ：

sleep Don't fit , Just let the naked eye see that it meets the conditions

  Out-of-service Thread.sleep  Alternate threads .

In fact, it is disorderly , Need to communicate with threads () To realize alternate printing of two threads .