"Java" Cubs first: Java basics

Zilong
Function: Display "Hello" in console
Date: 2017-04-11

Public: Indicates that the class is a common class, and that there can be only one publicly class in a Java file
Class: Indicates that this is a category
Hello: Class name (the class name of the public class must be the same as the file name)
public class Hello
{
A main function, equivalent to the entry of a program
public static void Main (String args[])//main function, only one main function in a common class
{
EXECUTE statement
System.out.println ("hello!");

/* int a=10; Define a variable, the variable name a, and its value 10
int b=20; Define a variable, variable name B, whose value is 20
int result=a+b;
Output results
SYSTEM.OUT.PRINTLN ("The result is" +result); */

Char char1= ' q ';
System.out.println (CHAR1);

int test1= ' A ' + ' B ';
System.out.println (test1);

Char test2= ' a ' + ' B ';
System.out.println (TEST2);

This violates the principle that data is converted from high-precision to low-precision.
Byte<short<int<long<float<double
In Java 3.4, 4.5 decimal is the default double data type

int a=1.2;
float a=3.4f;
System.out.println (a);

int a= (int) 1.2;
int b= (int) 1.9;
System.out.println ("a=" +a+ "b=" +b);

int a=1;
Double b=4.5;
A=b;
B=a;

int a=3;
int b=a+3.4;
System.out.println (b);
}
}

————————————————————————————————————————

The Java language provides eight basic types. Six types of numbers (four integers, two floating-point types), one character type, and one Boolean type.
1, integers: including int,short,byte,long
2. Float Type: float,double
3, Character: Char
4, Boolean: Boolean

Basic type	Size	Minimum value	Maximum Value
Boolean	-----	-----	------
Char	16-bit	Unicode 0	Unicode 2^16-1
Byte	8-bit	-128	+127
Short	16-bit	-2^15	+2^15-1
Int	32-bit	-2^31	+2^31-1
Long	64-bit	-2^63	+2^63-1
Float	32-bit	IEEE754	IEEE754
Double	64-bit	IEEE754	IEEE754
void

"Java" Cubs first: Java basics