First, the characteristics of Java:
1, Java simplicity
Compared with C language,
Core pointer of C language (save address) *p
There is no concept of pointer in Java (using the concept of reference)
2.Java is object-oriented (lazy thinking)
Class object interface
Object-oriented Feature: Encapsulated Inheritance Polymorphism
3.Java distribution
Double Eleven JD.COM Taobao/KLOC-000050 million visitors visited their servers.
If there are only 1 server, the pressure will be greater.
Multiple servers support the same service together.
4, Java cross-platform (system)
JDK program development package (including JRE and JVM)
The running environment of JRE program (including JVM)
Virtual machine Java virtual machine
Java code runs on a virtual machine.
Mac system installs a Mac version of JVM.
Windows system installs a windows version of JVM.
Java file suffix:. Java language (a computer language, especially for creating websites)
Note:. Java files cannot be run directly, and a compilation process is needed. Class files (files that a virtual machine can run).
5. Java security (memory)
Java memory processing mechanism:
GC garbage collection mechanism: delayed collection (delayed processing), at a certain moment, will be automatically collected by the system (round search).
6.Java robustness (make your website more fault-tolerant)
Java is a strongly typed language (strictly case sensitive).
Exception handling mechanism: prompt the user
Second, the basic knowledge of Java
At the beginning of java, you should first understand what identifiers are, the standardization of naming, and the meaning of basic lines of code.
1, * * Identifier in **java * *
Class name variable name interface name
Naming specification for identifiers
Can only start with the numeric letter underscore _ dollar sign $
2.* * Naming specification for class names: * *
Use big hump naming: the first letter of a word is capitalized, and the first letter of each word is capitalized when there are multiple words.
Small hump naming: (define variable name usage)
The first word is lowercase, and all words are capitalized except the first word.
Note: when naming a name, you must know the meaning of the name; Keywords in java: words with special meanings provided by the system (once used by the system, they can no longer be used).
3.* * Variables and constants * *
Constant: A constant is a quantity that will not change during the running of a program.
Variables: storing data
Data type variable name = initial value;
4.* * Data type: * *
First, the basic data types:
(1) Integer:
1.byte type: indicates that one byte (one byte is represented by eight binary bits) can store one byte of data.
2.short: a two-byte short integer.
# Integer (Universal): four bytes
4.long long: eight bytes.
(2) floating-point type:
1.float: four bytes.
2.double (by default, the decimal system generally declared uses double type): eight-character section.
3. Character type: Character
Features: Integer conversion can be used.
4. Boolean Boolean type:
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