程式碼重構那些事兒
大家好,這是我今天演講的目錄,分Java,JavaScript,ABAP三門程式語言來講述。
Java
•JAD
•javap
•Java Decompiler
•Source Monitor
•Visual VM
•Refactor Menu in Eclipse
ABAP
•Code inspector
•Refactor feature in AIE
•Code coverage
JavaScript
•ESLint for Fiori Apps
•Check Jenkins build log
•JSlint for Sublime Text 2
•Code check in WebIDE
•Profile in Chrome
在方法裡引入一個布林型別的引數控制方法的行為,這種做法正確嗎?
看看stackoverflow上是怎麼說的。
Java裡定義常量的最佳實踐:
http://developer.51cto.com/ar...
Java裡這兩種定義常量的方法,哪種更好?
package one; public interface Constants { String NAME = "孫悟空"; int BP = 10000; }
或
package two; public class Constants { public static final String NAME = "貝吉塔"; public static final int BP = 9000; }
為什麼我們不應該在Java 介面中使用Array:
https://eclipsesource.com/blo...
避免Array的原因之一:Array若使用不當,會造成效能問題
避免Array的原因之一:Array若使用不當,會造成效能問題
避免Array的原因之二:Array是面向過程程式設計領域的概念,使用Java面向物件的集合類,比如List,而不是Array
看個具體例子:
String[] array = { "喬布斯", "張小龍" }; List list = Arrays.asList( array ); System.out.println( list ); // 列印輸出 [喬布斯, 張小龍] System.out.println( array ); // -> [Ljava.lang.String;@6f548414 list.equals( Arrays.asList( "喬布斯", "張小龍" ) ) // -> true array.equals( new String[] { "喬布斯", "張小龍" } ) // -> false
看出差距了吧?
Arrays不是型別安全的!
下面的程式碼能通過編譯,但是執行時會報ArrayStoreException的異常:
Number[] numbers = new Integer[10]; numbers[0] = Long.valueOf( 0 );
而使用JDK的集合類比如List,就能在編譯器即檢測出這類錯誤。
Javascript裡有趣的逗號
function a() { console.log("I was called!"); return "Jerry"; } var b = a(), a;
然後執行下面的程式碼:
console.log(b);
會打印出Jerry
再看這段程式碼:
var d = (function c(){ return a(),a; })(); console.log(d);
會打印出:
I was called! function a() { console.log("I was called!"); return "Jerry"; }
再看這段程式碼呢?
(function() { var e = f = 1; })();
直接報錯:Uncaught ReferenceError: f is not defined
JavaScript裡有趣的分號
var b = function(para) { return { doSomething: function() { console.log("hello: " + para); return para; } } } var a = 1, x = 3, y = 4, s s = a + b (x + y).doSomething() // 打印出 hello: 7 console.log(s) // 打印出 8 function test(i){ var result = i++; return result } console.log("test: " + test(3)) // 打印出undefined
繼續看這段程式碼
s = function(x){ console.log("called: " + x ); return x} (1 + 2).toString() s = function(x){ console.log("called: " + x ); return x}(1 + 2).toString() // 打印出 called: 3
小技巧 - 如何把您自己增強邏輯植入到legacy遺留程式碼中
var bigFunction = function() { // big logic console.log("big logic"); // 這句話模擬我們在一段很冗長的遺留程式碼裡植入自己的新邏輯 } // 下面這種解決方案不會直接修改遺留函式本身,顯得比較優雅 var _old = bigFunction; bigFunction = function() { if ( _old ) { _old(); } console.log("our own enhancement"); } bigFunction(); // 第三種解決方案採用了面向切片程式設計思想,顯得更加高階 var bigFunction = function() { // big logic console.log("big logic"); } bigFunction = ( bigFunction || function() {} ).after( function() { console.log("our own logic"); }); bigFunction();
如何優雅的在一個函式裡增添效能測試統計的工具程式碼
var append_doms = function() { var d = new Date(); // dirty code - nothing to do with application logic!!! for( var i = 0; i < 100000; i++) { var div = document.createElement( "div"); document.body.appendChild(div); } // dirty code - nothing to do with application logic!!! console.log(" time consumed: " + ( new Date() - d)); }; function test() { append_doms(); }
傳統方案:在充滿了業務邏輯的函式體裡強行加入紅色標準的蒐集效能測試的工具程式碼,這個實現顯得很醜陋:
再看看採用面向切片程式設計思路的解決方案:AOP - Aspect Oriented Programming
var append_doms = function() { for( var i = 0; i < 100000; i++) { var div = document.createElement( "div"); document.body.appendChild(div); } }; var log_time = function( func, log_name) { return func = ( function() { var d; return func.before( function(){ d = new Date(); }).after( function(){ console.log( log_name + ( new Date() - d)); }); })(); }; function test() { log_time(append_doms, "consumed time: ")(); }
如何避免程式碼中大量的IF - ELSE 檢查
在呼叫真正的OData API之前,系統有大量的IF ELSE對API的輸入參宿進行檢查:
var send = function() { var value = input.value; if( value.length === '' ) { return false; } else if( value.length > MAX_LENGTH) { return false; } ... // lots of else else { // call OData API } }
更優雅的解決方案:
把這些不同的檢查規則封裝到一個個JavaScript函式裡,再把這些函式作為一個規則物件的屬性:
var valid_rules = { not_empty: function( value ) { return value.length !== ''; }, max_length: function( value ) { return value.length <= MAX_LENGTH; } }
實現一個新的檢查函式,變數檢查物件的屬性,執行校驗邏輯:
var valid_check = function() { for( var i in valid_rules ) { if ( vali_rules[i].apply( this, arguments) === false ) { return false; } } }
現在的OData呼叫函式非常優雅了:
var send = function( value ) { if ( valid_check( value ) === false ) { return; } // call OData API }
通過這種方式消除了IF ELSE。
另一種通過職責鏈 Chain of Responsibility 的設計模式 design pattern消除IF ELSE分支的程式碼重構方式:
先看傳統方式的實現:
// Priority: ActiveX > HTML5 > Flash > Form(default) function isActiveXSupported(){ //... return false; } function isHTML5Supported(){ //... return false; } function isFlashSupported(){ //... return false; }
好多的IF -ELSE啊:
var uploadAPI; if ( isActiveXSupported()) { // lots of initialization work uploadAPI = { "name": "ActiveX"}; } else if( isHTML5Supported()) { // lots of initialization work uploadAPI = { "name": "HTML5"}; } else if( isFlashSupported()) { // lots of initialization work uploadAPI = { "name": "Flash"}; } else { // lots of initialization work uploadAPI = { "name": "Form"}; } console.log(uploadAPI);
再看職責鏈設計模式的實現:
Chain of Responsibility
var getActiveX = function() { try { // lots of initialization work return { "name": "ActiveX"}; } catch (e) { return null; } } var getHTML5 = function() { try { // lots of initialization work return { "name": "HTML5"}; } catch (e) { return null; } }
程式碼整潔優雅:
var uploadAPI = getActiveX.after(getHTML5).after(getFlash).after(getForm)(); console.log(uploadAPI);
Java中的String
public class stringTest { public static void main(String[] args) { String userName = "Jerry"; String skill = "JS"; String job = "Developer"; String info = userName + skill + job; System.out.println(info); } }
用javap將上面的Hello World程式反編譯出來學習:
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