__2017-12-16 如一模式识别研究

如一模式识别研究

JAVA>>编写高质量代码改善java程序的151个建议——[1-3]基础?亦是基础

转自:http://www.cnblogs.com/Alandre/p/3755822.html

           原创地址: http://www.cnblogs.com/Alandre/ (泥沙砖瓦浆木匠),需要转载的,保留下! Thanks

The reasonable man adapts himself to the world;the unreasonable one persists in trying to adapt the world to himself. —萧伯纳

相信自己看得懂就看得懂了,相信自己能写下去,我就开始写了.其实也简单—泥沙砖瓦浆木匠

Written In The Font

Today , I am writing my java notes about <编写高质量代码改善java程序的151个建议> -秦小波.

Three pieces[1-3]:

1.Don't code by confusing letters in the constants and variables [不要在常量和变量中出现易混淆的字母]

2.Don't change the constants into the variable. [莫让常量蜕变成变量]

3.Make the the types of ternary operators the same. [三元操作符的类型务必一致]

Don't code by confusing letters in the constants and variables

from the book:

public class Client01 {

public static void main(String [] args)

{

long i = 1l;

System.out.println("i的两倍是:"+(i+i));

}

}

Outputs:

1

2  

(unbelieved?just ctrl c + ctrl v run the code !)

In my words:

‘1l’is not ‘11’. But we always code by the confusing things . then bebug for a long time , finally we will laught at ourselves with the computer and codes face to face.”What fucking are the coder?”lol,smile ! carm down , because u r so lucky to read this . i will tell some excemples to keep them away. away ? really away?

Step 1: somthing about Coding Standards

★Constants should always be all-uppercase, with underscores to separatewords. [常量都要大写,用下划线分开]

See a case from my project ITP:

package sedion.jeffli.wmuitp.constant;

public class AdminWebConstant

{

public static final String ADMIN_BASE = "/admin";

public static final String WEB_BASE = ADMIN_BASE + "/web";

/**

* view

*/

public static final String ADMIN_LOGIN_VIEW = WEB_BASE + "/login";

public static final String ADMIN_INDEX_VIEW = ADMIN_BASE + "/index/index";

/**

* 返回String状态

*/

public static final int RESULT_SUCCESS = 1;

public static final int RESULT_FAIL = 0;

}

★Camel Case:[变量命名驼峰原则,自然你也可以选择其他的法则等]

if u wanna do it , right now ! it can make your codes more beautiful and clean! amazing ! u learned it , keep on!!!

package sedion.jeffli.wmuitp.util;

import javax.servlet.http.HttpSession;

import sedion.jeffli.wmuitp.entity.TeacherInfo;

import sedion.jeffli.wmuitp.entity.UserLogin;

public class AdminUtil

{

public static final String ADMIN = "admin";

public static final String ADMIN_ID = "adminID";

public static final String TEACHER_ID = "teacherID";

public static void saveAdminToSession(HttpSession session,UserLogin userLogin)

{

session.setAttribute(ADMIN, userLogin);

}

public static void saveAdminIDToSession(HttpSession session,UserLogin userLogin)

{

session.setAttribute(ADMIN_ID, userLogin.getUlId().toString());

}

public static UserLogin getUserLoginFromHttpSession(HttpSession session)

{

Object attribute = session.getAttribute(ADMIN);

return attribute == null ? null : (UserLogin)attribute;

}

public static String getUserLoginIDFromHttpSession(HttpSession session)

{

Object attribute = session.getAttribute(ADMIN_ID);

return attribute == null ? null : (String)attribute;

}

}

#please remeber the camel , then u can write a nice code.

Step 2: somthing can make your program easier to understand

some letters should not be used with the numbers,like l O … they are the brother of the numbers.but we can do some to avoid. like use ‘L’ , and write some notes about them.

Don't change the constants into the variable

A magical demo:

public class Client02

{

public static void main(String [] args)

{

System.out.println("const can change: "+ Const.RAND_COSNT);

}

//接口常量

interface Const

{

public static final int RAND_COSNT = new Random().nextInt();

}

}

#I think the demo is bad. RAND_COSNT is not a constant and we never do that.

what is Constants ?

Constants are immutable values which are known at compile time and do not change for the life of the program.But if the project is too large to manage.There will be a problem.Let me show u!

example:

//file: A.java

public interface A

{

String goodNumber = "0.618";

}

//file: B.java

public class B

{

public static void main(String [] args)

{

System.out.println("Class A's goodNumber = " +A.goodNumber);

}

}

Outputs:

Class A's goodNumber = 0.618

Now we change A.java –> goodNumber to “0.6180339887”

//file: A.java

public interface A

{

String goodNumber = "0.6180339887";

}

“javac A.java”then “java B” , we will find the outputs is the same:

Class A's goodNumber = 0.618

why??????????????????

just see the class of B, use “ javap –c B”:

Compiled from "B.java"

public class B {

public B();

Code:

0: aload_0

1: invokespecial #1 // Method java/lang/Object."":()V

4: return

public static void main(java.lang.String[]);

Code:

0: getstatic #2 // Field java/lang/System.out:Ljava/io/PrintStream;

3: ldc #3 // String Class A's goodNumber = 0.618

5: invokevirtual #4 // Method java/io/PrintStream.printl

n:(Ljava/lang/String;)V

8: return

}

#3: ldc #3 // String Class A's goodNumber = 0.618

ok , we see! the last interface A was already in the class B. so we can “javac B.java”to deal.

All in all ,

Java Interface is usually the best place to store The Constants.

[Java Interface 通常是常量存放的最佳地点]

A best way store constants : static fianl XXX static Object getXXX()

it shows the Java dynamic advantage and a constant principle.

//file:A.java

public class A

{

private static final String goodNumber = "0.6180339887";

public static String getGoodNumber()

{

return goodNumber;

}

}

//file:B.java

public class B

{

public static void main(String [] args)

{

System.out.println("Class A's goodNumber = " +A.getGoodNumber());

}

}

Make the the types of ternary operators the same.

from the book:

public class Client03 {

public static void main(String[] args) {

int i = 80;

String s = String.valueOf(i<100?90:100);

String s1 = String.valueOf(i<100?90:100.0);

System.out.println(" 两者是否相等:"+s.equals(s1));

}

}

Outputs:

1

false

  

see the compiled code ,use “javap –c Client03”,we will see:

23: if_icmpge 32

26: ldc2_w #3 // double 90.0d

29: goto 35

32: ldc2_w #5 // double 100.0d

the transformation rules about ternary operators.

三元操作符类型的转换规则:

1.若两个操作数不可转换,则不做转换,返回值为Object 类型。

2.若两个操作数是明确类型的表达式(比如变量),则按照正常的二进制数字来转换,int 类型转换为long 类型,long 类型转换为float 类型等。

3.若两个操作数中有一个是数字S,另外一个是表达式,且其类型标示为T,那么,若数字S 在T 的范围内,则转换为T 类型;若S 超出了T 类型的范围,则T 转换为S类型(可以参考“建议22”,会对该问题进行展开描述)。

4.若两个操作数都是直接量数字(Literal) ,则返回值类型为范围较大者。

Editor's Note

合抱之木,生于毫末;九层之台,起于累土;千里之行,始于足下. ---老子<<道德经>>

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