JAVA introductory system tutorial (3) Basic syntax (1)
1. Keyword: a word given a specific meaning by the Java language (the letters that make up the keyword are all lowercase)
1) Use Keywords for defining data types
class, interface, byte, short, int, long, float, double, char, boolean, void## 2 ) Used to determine the data type value keyword
true, false, null
3) Used to define process control Keywords
if, else, switch, case, default, while, do, for, break, continue, return
4) Use Keywords used to define access permission modifiers
private, protected, public
5) Used to define class, function, variable modifiers Keywords
abstract, final, static, synchronized
## 6) Keywords used to define the relationship between classes
extends, implements
7) Keywords used to define the creation of instances, reference instances, and determine instances
new, this, super, instanceof
8) Keywords used for exception handling
try, catch, finally, throw , throws
9) Keywords used for packages
package、import
10 ) Other modifier keywords
native, strictfp, transient, volatile, assert
##2. Identifier: for classes, excuses, Character sequence used when naming methods, variables, etc.
(ps: must be English uppercase and lowercase letters, numeric characters, ￥ and _)
Note: It cannot start with a number; it cannot be a keyword in java; Java is strictly case-sensitive
3. Comment: Text used to describe the program
1) Single line comment: //annotation text
2) Multi-line comment: /*&*/
3) Documentation comments: /**&*/
##In order to have a It is a good habit for beginners to write comments first and then code when writing programs.
4. Constant: Its value cannot be changed during the execution of the program
String constant Content enclosed in double quotes
Integer constants All integers Decimal constants All decimals Character constants Contents enclosed in single quotes 5. Variable: During the execution of the program, the amount that its value can change within a certain range Data type variable name = initialization value; 6. Data type: Java language is a strongly typed language. Each type of data has a clear and specific data type defined, and different sizes of memory space are allocated in the memory Precautions for using variables: Example question: System.out.println('a'); System.out.println(5 5 ”=5 5”); Observe the above output #END #Related articles: JAVA entry system tutorial (1) Configuring the JAVA development environment
##JAVA entry system tutorial (2) Installing and using eclipse
Boolean constants are more unique, only true and false
Empty constants Null (explained in the array part)
Note: The format is fixed, remember the format, and adapt to changes 
Scope: In which level of braces the variable is defined, the scope of which brace is the scope of the variable. Two variables with the same name cannot be defined in the same scope.
Initialization value: Cannot be used directly without initialization value
It is recommended to define only one variable on a line, you can define multiple, but it is not recommended
System.out.println('a' 1);
System.out.println("hello" 'a' 1 );
System.out.println('a' 1 ”hello”);
System.out.println(“5 5=" 5 5);
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