"2014-11-17" Java Learning note

2. Static indicates that main () can still run without creating a class object.
4. Java programs are made up of classes.
6. The file name of the original program cannot be arbitrarily named, it must be the same as the public class name, so in a separate primitive program, there is only one public class, but there can be many non-public classes.
8. Data type
1. Byte:1 byte
2. Short:2 bytes
3. Int:4 bytes
4. Long:8 bytes
5. Float:4bytes
6. Double:8 bytes
7. Char:2 bytes
8. Boolean
10. Operator
1. Assignment operator: =
2. Unary operators: + 、-、! , ~
3. Arithmetic operators: + 、-、 *,/,%
4. Relational operators:
5. Increment decrement operator
6. Logical operators:&&, | |
7. Parentheses operator: ()
12. Array:
1. Declaration of one-dimensional array: int socre[]; Score = new Int[3];
2. Array copy: System.arraycopy (source,0,dest,0,x)
3. Array sort: Arrays.sort () (Import java.util.*)
4. Declaration of a two-dimensional array: int score[][] = {{},{},{}};
14. Class
2. Object declaration: Class Name Object name = new class name ();
4. Comparison of objects:
1. = =: Used to compare memory address values of two objects for equality
2. Equals (): Used to compare the consistency of the contents of two objects
6. Object array: Person p[]; p = new Person[3];
8. Final keyword
1. The final tagged class cannot be inherited
2. Final tagged methods cannot be overridden by a quilt class
3. A variable of the final tag is a constant and can only be assigned once
10. Static keyword
1. static variables
2. Static methods
12. instanceof Keywords
1. Determines whether a class implements an interface, or whether an instance object belongs to a class.
14. Java Common class libraries
1. String class and StringBuffer class
2. System class and Runtime class
16. Package and access rights
1. Package Statement: Package Name.java
2. Package Imports: Import Package name. Class names
3. JDK Common Packages
1. Java.lang contains some of the core classes of the Java language, such as String, Math, Integer, System, and thread.
2. java.awt contains multiple classes that make up an abstract window toolset for building and managing the application's graphical user interface (GUI)
3. Avax.swing is used to build a graphical user interface, which is a lightweight component relative to the java.awt package.
4. Java.applet
5. The java.net contains the operation classes that perform network-related operations.
6. java.io classes that provide multiple input/output functions.
7. Java.util contains some utility classes.
18. Access control permissions for class members
2. Private: The member method or member variable can only be used inside this class.
4. Default: Access control members can be accessed by other classes in this package.
6. Protected: This member can be accessed either by another class in the same package or by a subclass in a different package
7. Public: can be accessed by all classes, regardless of whether the access class is within the same package as the class being accessed.

   	Private	Default	Protected	Public
   Same class	√	√	√	√
   Classes in the same package		√	√	√
   Subclasses in different packages			√	√
   In the other package				√

20. Java Naming conventions
1. The letters in the package name are all lowercase
2. Class name, interface name should use nouns, capitalize each word first letter
3. Variable name the first word lowercase, followed by the first letter of each word capitalized
4. The first word of the method name is lowercase and the first letter of each word is capitalized
5. Every letter in a constant name is capitalized
22. File IO operations
1. File class: The file class is the only object in the IO package that represents the disk file itself.
1. GetName () returns the file name
2. GetParent () returns the parent directory name
3. Exists () file exists
2. Randomaccessfile class
3. Stream class
1. Inputstream,outputstream,fileinputstream, FileOutputStream: Byte stream Class (processing bytes or binary objects)
2. Reader,writer, FileReader, FileWriter: Character Stream Class (handles characters or strings)
3. Pipe flow: PipedInputStream, PipedOutputStream, Pipedreader, PipedWriter
4. Print Flow: system.in, System.out
5. Redirection and piping
   1. % Java Average < data.txt//redirecting from a file to standard input
   2. % java randomseq 200.0 > data.txt//redirecting Standard output to a file
   3. % java RANDOMSEQ 1000 200.0 | Java Average//piping The output of one program to the input of another

"2014-11-17" Java Learning note