Shulou(Shulou.com)06/02 Report--

What this article shares with you is about the basic data types of JAVA. The editor thinks it is very practical, so I share it with you to learn. I hope you can get something after reading this article. Let's take a look at it.

1: keyword (master)

(1) words with specific meanings given by Java language

(2) characteristics:

All lowercase.

(3) Note:

A:goto and const exist as reserved words.

B: advanced notepad like Notepad++ will have special color markings for keywords

2: identifier (master)

(1) A sequence of characters that give names to classes, interfaces, methods, variables, etc.

(2) composition rules:

A: uppercase and lowercase letters

B: number

CRV $and _

(3) Note:

A: you can't start with a number

B: cannot be a keyword in java

C: case sensitive

(4) Common naming rules (see name)

A: all lowercase packages

Single-level package: lowercase

For example: liuyi,com

Multi-level package: lowercase, and use. Separate

For example: cn.itcast,com.baidu

B: class or interface

One word: first letter capitalized

For example: Student,Demo

Multiple words: the first letter of each word is capitalized

For example: HelloWorld,StudentName

C: methods or variables

One word: lowercase initials

For example: name,main

Multiple words: starting with the second word, the first letter of each word is capitalized

Example: studentAge,showAllNames ()

D: constant

All uppercase

One word: uppercase

For example: PI

Multiple words: uppercase and separated by _

For example: STUDENT_MAX_AGE

3: comments (master)

(1) it is the text that explains the program.

(2) Classification:

A: single-line comments / /

B: multiline comments / * /

C: documentation notes (later) / *

(3) write an annotated version of the HelloWorld case.

Later, we are going to write a program process.

Demand:

Analysis:

Achieve:

The code reflects:

(4) the function of notes

A: explain the program and improve the readability of the code.

B: it can help us debug the program.

Later, we will explain a more high-end debugging tool.

4: constant (master)

(1) the amount by which the value does not change during the execution of the program

(2) Classification:

A: literal constant

B: custom constants (later)

(3) literal constant

A: string constant "hello"

B: integer constant 125.23

C: decimal constant 12.345

D: the character constant 'axiomagery'

E: Boolean constant true,false

F: empty constant null (later)

(4) there are four representations for integer constants in Java.

A: the binary system consists of 0Pol 1. It starts with 0b.

B: the octal is made up of 0pl. 7. Start with 0.

C: the decimal system consists of 0pm 1pm .9. Integers default to decimal.

D: the hexadecimal system is made up of 0meme 1pm .9pm a recorder, b recorder, c recorder, d recorde f (both uppercase and lowercase). It starts with 0x.

5: binary conversion (understanding)

(1) other binary to decimal

Coefficient: the value on each bit

Cardinality: the cardinality of the x base is x

Weight: for each bit of data, from the right, and starting from 0, the corresponding number is the weight of the data.

Result: the sum of the coefficient * cardinality ^ power.

(2) Decimal to other base systems

Except the base takes the remainder until the quotient is 0, the remainder is reversed.

(3) Fast conversion method of binary conversion

A: conversion between decimal and binary

8421 yards.

B: binary to octal, hexadecimal conversion

6: variables (mastery)

(1) the amount by which the value of the program can be changed within a certain range during the execution of the program

(2) the definition format of variables:

A: data type variable name = initialization value

B: data type variable name

Variable name = initialization value

7: data type (master)

(1) Java is a strongly typed language that provides a corresponding data type for each type of data.

(2) Classification:

A: basic data types: 4 categories and 8 kinds

B: reference data types: classes, interfaces, arrays.

(3) basic data types

A: integer occupancy of bytes

Byte 1

Short 2

Int 4

Long 8

B: floating point number

Float 4

Double 8

C: character

Char 2

D: Boolean

Boolean 1

Note:

Integer defaults to int and floating point defaults to double.

Add L or l to long integers.

F or f should be added to single-precision floating-point numbers.

8: data type conversion (master)

(1) boolean type does not participate in conversion

(2) default conversion

A: from small to big

Int-long-float-double

The int type is directly converted to participate in the operation without converting each other.

(3) forced conversion

A: from big to small

B: there may be a loss of accuracy, which is generally not recommended.

C: format:

Target data type variable name = (target data type) (converted data)

(4) thinking questions and interview questions:

A: is there any difference between the following two ways?

Float F1 = 12.345f

Float f2 = (float) 12.345

B: is there anything wrong with the following procedure? if so, where is it?

Byte b1 = 3

Byte b2 = 4

Byte b3 = b1 + b2

Byte b4 = 3 + 4

C: what is the result of the following operation?

Byte b = (byte) 130

D: characters participate in operation

Is to find the value in ASCII

'a' 97

'A' 65

'0' 48

System.out.println ('a')

System.out.println ('a' + 1)

E: string participating in operation

This is actually a string connection.

System.out.println ("hello" + 'axioms 1)

System.out.println ('astatine 1 + "hello")

System.out.println ("5x 5 =" + 5x 5)

System.out.println (5x5+ "= 5x5")

These are the basic data types of JAVA, and the editor believes that there are some knowledge points that we may see or use in our daily work. I hope you can learn more from this article. For more details, please follow the industry information channel.

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