Java basic content;
1) keywords in Java:
Common keywords for the future:
Class,public,static (Object-oriented section), the key word in the Process Control statement: If,else.
Basic data type: Int,byte,short ...
Synchronized (in multi-threaded)
2) Identifier: A sequence of characters that give a class, interface, variable, or method a name
3) Package Name: Single-level package (single directory)/multi-level package (multi-level directory) (often used)
4) class/interface: Single word: Capitalize the first letter of the word
A) Multiple words: Capitalize the first letter of each word:
Method: Single word: all lowercase letters
Multiple words: First word lowercase, starting with the second word each word capitalized (printxing ())
b) Constants: Single word: All uppercase letters
Multiple words: All uppercase letters, separated by underscores between words and words
5) Variables:
1> three elements: 1) data type 2) variable name 3) initialization value;
A) Classification of data types:
Basic data type: 4 in Class 8
1. Integer type
a>; BYTE range -128~127
b>; Short
c>; INT--The wrapper class type for the base data type-?int (reference type): Integer
d>; Long
2. Floating-point type float double
3. Character type: Char---? basic type-? Reference type: Character
4. Boolean Type: Boolean
attention to content;
1) Default type promotion: Byte,short,char do not convert, once participate in the operation? int type
2) Forced type conversion: According to the specific needs to use, it is recommended to try not to force the type conversion, it loses the accuracy of the data!
Target data type variable name = (target data type) (variable value);
3) Mastery: When "+ Becomes string concatenation": string + any data = new string
"Hello" +1+ ' 0 ' = hello1 (string concatenation)
"Hello1" + ' 0 ' =hello10
' 0 ' +1+ "Hello" = 49hello (at this time 0 because there is a single quotation mark, the ASCLL code table of 48, ' 0 ' +1 this plus becomes the operator, 48+1==49, and then + "Hello", at this time + is "string concatenation character")
Three values in the ASCII code table: When the character participates in the operation, it will find his corresponding value in the table.
' 0 ' ~48
' A ' ~97 (A-Z can be launched yourself)
' A ' ~65 (A-Z can be launched yourself)
Two; operators
The operators are divided into:
1. Arithmetic operator: extended operator: ++/--
2. Assignment operator: +=,/=,*= (extended assignment operator), hiding forced type conversions
3. Comparison operator: "= =" (different from "=" meaning, "= =" before equals = = equals sign, "=" is the assignment after the equal sign to the equal sign)
4. Logical operators: logical double and &&, logical double or | |
{logical double and &&: With short-circuit effect, if the condition expression on the left is false, then the right side does not execute
Logical Double or | | : Has a short-circuit effect, if the condition expression on the left is true, then the right side does not execute}
7. Ternary operators:
(conditional expression)? True result: false result;
III. Process Control Statements
Process Control statements are divided into;
1. Sequential structure;
The code starts from the top down;
2. Select the structure;
1> If statement:
Format 1:if (expression) {...}
Format 2: Actual development, use the most, for two conditions to judge
if (expression) {
...
}else
2> Switch statement
3. Cyclic structure
The cyclic structure is divided into;
1>.for Cycle
for (initialization statement; Conditional statement; Step statement) {
loop body statement;
}
2>.while cycle;
A> while (conditional expression) {
Loop statement Body
}
B> Extended format: (better than basic format)
initialization statements;
while (conditional expression) {
loop body statement;
Step statement;
}
3>.do while loop
The third type of a> LOOP statement structure:
Do-whle:
Basic format
do{
loop body statement;
}while (conditional statement, step statement);
C> Extended Format:
initialization statements;
do{
loop body statement;
Control Body Statement;
}while;
4> double-layer for loop
For loop nesting:
For (initial value, conditional statement, step statement)
{
For (initial value, conditional statement, step statement)
{
loop body content statement;
}
}
Four, jump control statements
1) Break: means interruption, end meaning, concluding sentence;
Break: cannot be used alone, typically in a switch statement, or in a loop statement
2) Continue: Interrupt can continue execution of the following loop (jump out of the current loop, directly into a loop)
Continue: Use multiple in a looping statement (cannot be used alone)
3) Retrun: Return value of method, bring back a result
public static return value method name (parameter type 1 variable 1, parameter type 2 variable name) {
Return
}
Permission modifier: public + static (static adornment) method is static and is a common method
Return type: What data type is the result of the final calculation and (what data type is the result of that type of acceptance)
Method Name: Is the code block for this function name: Naming rules: A word letter all lowercase; multiple words: the first word is lowercase, the second word starts with an uppercase letter;
Return: A line in a method indicating that a result is brought back
A> Method Invocation:
1) Separate calls
a> separate call, no meaning, no output results
B> when the demand, the shape is directly output in the console, no specific return value, but also conform to the method specification,---> Keywords: void substitution syntax return value
C> does not have a specific method for returning values, and is suitable for individual invocation
2) Output Call
Direct output of the results, write dead, can not operate on the results
3) Assignment invocation: A method with a return value type, which is recommended to use an assignment call, which can result in further action
B> Precautions:
1) methods and methods are lateral relationships, and a method can no longer define a method
2) When defining a method, the formal parameter must have a data type, otherwise there is a problem
3) in main main (), when invoking a method, the actual parameter does not need a data type
4) Where there are curly braces, there can be no semicolon, there is no curly brace where there is a semicolon
Interview questions?
What is the difference between break and continue?
1.break jumps out of the total loop, no longer executes the loop (ends the current loop body);
2.continue jumps out of the loop and proceeds to the next loop (ending the loop that is being executed and entering the next loop condition);
Summary of basic Java learning content
