Java Syntax Basics

1, Keyword: In fact, a language has given special meaning to the word.

Reserved words: In fact, there is no special meaning, but prepare the words to be used later.

2, identifier: is actually a custom noun in the program. such as the class name, variable name, function name. Contains 0-9, A-Z, $, _;

Attention:

1), the number may not begin.

2), the keyword cannot be used.

3, constant: is the data that does not change in the program.

4, variable: In fact, is a storage space in memory, used to store constant data.

Function: Convenient for operation. Because some data is uncertain. So determine the noun and storage space for the data.

Features: Variable space can be reused.

Scope of the variable:

The scope starts at the position defined by the variable and ends with the curly brace where the variable is located;

Data type:

1): Basic data type: Byte, short, int, long, float, double, char, Boolean

2): Reference data type: Array, class, interface.

Automatic type conversion: from low to high level, the system automatically turn;

Coercion type conversions: When to use? Assign a high-level number to a variable that has a low rank for that number;

Operation Symbols:

1), arithmetic operator.

+-*/%: Any integer modulus 2 is not 0 is 1, so as long as the change is the module can be implemented switch operation.

+: Connector.

++,--

2), assignment operator.

=  += -= *= /= %=

3), comparison operator.

Features: This operator is characterized by the result of the operation, either True or false.

4), logical operator.

& |   ^  ! && | |

Logical operator except! are used to concatenate two Boolean expressions.

&: Only both sides are true and the result is true. Otherwise, it is false.

|: If both sides are false the result is false, otherwise it is true

^: xor: And or a little different.

On both sides, the result is false.

It is true that the results are different on both sides.

& and && difference: &: Whatever the left result is, the right side is involved in the operation.

&&: Short circuit with, if the left is false, then the right side is not a parameter and operation.

| and | | Difference: |: Both sides are calculated.

|| : Short circuit or, if the left is true, then the right side does not participate in the operation.

5), bitwise operator: operator used to manipulate bits.

& | ^

<< >> >>> (unsigned Right shift)

5, statement.

If switch do and while and for

Switch (variable) {

Case value: The statement to be executed;

...

Default: the statement to execute;

}

How it works: compare the values of the variables in parentheses with the values after the case, and the values after the case are the same

Executes the statement following the case, and if there is no same, execute the statement after the default;

Details: 1): Break can be omitted, if omitted, has been executed until a break is encountered;

2): The variable in parentheses after switch should be one of the byte,char,short,int four types;

3): Default can be written anywhere in the switch structure, if the default statement is placed in the first row, regardless of whether expression matches value in case, the program starts execution from default until the first break occurs.

The loop structure is used when some statements need to be executed many times.

While and for can be interchanged.

The difference is that if you need to define a variable control loop number. It is recommended to use for. Because the For loop is complete, the variable is freed in memory.

Break: Acts on a switch, and a loop statement, used to jump out, or to be called an end.

Continue: Only for loop structure, continue to recycle.

Effect: End this cycle and continue the next cycle. When the statement is present alone, the statement below cannot be defined and cannot be executed.

Java Syntax Basics