Learning content:
1. Java Language Foundation
Keywords (all letters are lowercase)
class//class
interface//interface
byte//byte bit: bit
short//short-Integer 2 byte
int//Integral type 4 bytes
long//Long integer 8 bytes
float//floating Point type
double//double-precision floating point.
char//characters
boolean//Boolean false True
void//Empty
null//empty, not present
if//if
esel//otherwise
switch//Branch
case//situation.
default//default, default
while//when ... Cycle
do//
For//for Cycle
break//Interrupt
continue//continue
return//return
[Access rights control]
private//Private
proected//protected
public//the public
[Class function Modifier]
abstract//Abstract
final//the final
static//Static
Synchronized//Sync
extends//extension
implements//implementation
new//New
this//Current
SUPER//Super class, parent class,
Whether instanceof//is an instance of XXX
try//try
catch//capture
finally//final
throw//throws
throws//throws an exception when defining a class declaration
package//Bag
import//Import Export
native//the Local
transient//instantaneous, temporary, temporary persistent.
asset//Assertion
Specification of custom identifiers, note that Java is strictly case-sensitive;
Note: single-line comment//, multiline comment/* */, document comment/** */(Javadoc), develop good habit of writing notes;
2, constant, can not be changed,
1, integer constant. All integers
2, decimal constant. All decimals
3, Boolean type constant. More unique, only two values. True false.
4, character constant. A numeric letter or symbol is identified by a single quotation mark (' ').
5, string constant. Identifies one or more characters in double quotation marks ("").
The 6,null constant. There is only one value: null.
3, integer four types of representation
Binary: 0,1, full 2 in 1
Octal: 0-7, full 8 in 1. Start with a 0 representation
Decimal: 0-9, full 10 in 1
Hex: 0-9,a-f, full 16 in 1. Start with a 0x representation
Conversion between the binary, weight,
Negative numbers are expressed in the form of the complement of the original code, and the positive and negative numbers are added 0, overflow the highest bit, exactly equal to 0;
-128 in the memory of the binary is 1000 0000, can be obtained by 127-1;
All the binary if each is 1, then its real data is-1;
Positive numbers also support the complement, which is consistent with the source code;
Positive numbers can be negative minus one negation;
How to get the binary representation of a negative number quickly by a positive number: starting from the lowest bit the same until the first 1 you meet, the back of all the reverse.
4, variable, used to keep the same type of constant, and can be reused
Define the format of the variable: data type variable name = Initialize value
5, Java is a strong type, for each data type in memory allocated a different size of memory space
Basic data types
BYTE, short, int (positive default), long, float (decimal default), double, Char, Boolean
Reference data type
class, interface, []
Automatic (implicit) type conversion
Forcing (explicit) type conversions
6, Operator: arithmetic operator, assignment operator, comparison operator, logical operator, bitwise operator, ternary operator
Java is strongly typed, so the result of its operation and real life is somewhat different, in order to preserve the original memory, the underlying will do automatic conversion, discard high, only retain their own number of bits;
Permissions calculation Model: Logical Operations &, | To improve the efficiency of operations, such as the design of LIUNX systems.
Logic Operations &, | Why there is no short circuit: because it is converted to bits operations, bit operations require both sides to participate.
7. Program Flow Control
Judging structure
If Else
Switch
Loop structure
While
Do While
For
8. Functions
Modifier returns a value type function name (parameter type form parameter 1, parameter type parameter 2, ...)
{
Execute the statement;
return value;
}
Functions can only be called, and functions cannot be defined inside a function;
function overloading (number and type of arguments), variable parameters ...
Questions to help:
The permissions calculation model is still not quite clear!!!
Java Basics-Day 2nd