IDEA Inspections詳解

以前用Eclipse的時候就特別喜歡琢磨eclipse的warning級別(黃歎號)，以期待coding出最模範的代碼。

換成IDEA後，發現其代碼檢查功能更加複雜，遂仔細琢磨分析，尋找最適合本身的配置

Abstraction issues

Title	默認	建議	描述
'instance of' a concrete class		warning	instance of通常判斷是不是一個接口或者抽象類的實例
'instance of' check for this		warning	使用this確定知道是哪一個Class
Magic number		warning	不容許任何魔法值(即未經定義的常量)直接出如今代碼中 ，參考阿里規範
Overly strong type cast		warning	高強強制類型轉換，有時候咱們強轉List便可卻強轉成ArrayList

Assignment issues 

Title	默認	建議	描述
Assignment to for 'loop' parameter		warning	在for循環中改變了循環的參數
Constructor assigns value to field defined in superclass		warning	在構造方法中對父類成員變量賦值，這樣作不合理，應該調用父類構造方法

Class Metrics

Title	默認	建議	描述
Class with too many constructors		warning	類的構造方法過多（默認限制5個）

Class structure

Title	默認	建議	描述
Class name differs from file name		warning	類名和文件名不一樣
No-op method in abstract class		warning	抽象類中的空方法沒有被聲明成abstract，比較少見
'protected' member in final class		warning	定義成final的類沒法被繼承，protected的使用不正確

Code maturity

Title	默認	建議	描述
Call to printStackTrace()		warning	成熟的代碼應該使用log
Call to Thread.dumpStack		warning	靜態dumpstack()方法提供一個new exception ("stack trace").printstacktrace ()的封裝，打印一個追蹤當前線程的堆棧，調試用。
Use of absolute collection type		warning	使用了java.util.Vector or java.util.Hashtable這些不推薦使用的類
Use of System.out or System.err		warning	使用了System.out or System.err，用log替代

Code style issues

Title	默認	建議	描述
Blocker marker comment		warning	註釋位置不合理 while (i < 10) { i++; } // end while參考阿里規範，寫在while上方
C-style array declaration	No high lighting,only fix	warning	C語言風格的數組聲明 public String process(String value[])[] { return value; }
Control flow statement without braces	No high lighting,only fix	warning	條件或者循環語句括號沒打好
(expression).equals("literal")rather than("literal").equals(expression)		warning	減小空指針的好習慣
indexOf expression is replacable with contains		warning	Reports any List.indexOf() expressions which can be replaced with the method List.contains().
Missorted modifiers		warning	修飾詞順序不符合規範
Multiple variables in one declaration		warning	一行代碼聲明瞭多個變量
Redundant no-arg constructor		warning	多餘的無參構造方法
size==0 replacable with isEmpty		warning	很實用，判斷list非空isEmpty一目瞭然
Unnessarily null check before equals call		warning	多餘的空指針校驗
Variables of different types in one declaration		warning	一行聲明多個不一樣類型的變量，String s = "", array[];

Compiller issues

Title	默認	建議	描述
Unchecked warning	warning	無	不少check多餘，可關閉此warning

Control flow issues

Title	默認	建議	描述
Boolean expression could be replaced with conditional expression		warning	Boolean類型表達式優化 Reports any boolean expressions which can be expressed more compactly, and arguably more clearly, as a conditional expression. Take for example the following expression: a && b || !a && c; which may be expressed as: a ? b : c;
Conditional can be pushed inside branch expression	No high lighting,only fix	warning	條件表達式優化 Reports conditional expressions with then and else branches so similar that the conditional expression can be pushed inside, thereby shortening the code. For example the following conditional expression: condition ? message("value: " + 1) : message("value: " + 2) Can be pushed inside and transformed into: message("value: " + (condition ? 1 : 2))
default not last case in switch statement		warning	在switch中，default不在最後
duplicate condition in if statement		warning	if中出現了重複的條件
duplicate condition on && or ||		warning	條件重複
fallthrough in switch statement		warning	swich中未使用break
if statement could be replaced with conditional expression		warning	三元運算符簡寫if
if statement with negated condition		warning	if的條件是否認，能夠調換if else順序
negated equality expression		warning	!(i == 1)
pointless indexOf comparison		warning	indexOf>-1則無心義
redundant if statement	warning	無	多餘的if For example: if (foo()) { return true; } else { return false; } can be simplified to return foo(); 有時候爲了邏輯清晰，會有這樣寫的必要
switch statement without default branch		warning	switch缺乏default

Declaration redundancy

Title	默認	建議	描述
Declaration access can be weaker	warning	無	能夠定義更低的訪問權限public->protected->default->private， 但長遠考慮有時候會有這方面須要
Declaration can have final modifier	warning	無	聲明能夠加上final
Empty method	warning	無	空方法
Method can be void	warning	無	方法能夠聲明成void的， 雖然返回值沒用起來，可是將來極可能會被使用
Method returns the same value	warning	無	方法返回值老是相同，很常見
remove redundant lambda parameter types	No high lighting,only fix	warning	優化lambda參數自動推測 Example: Map<String, Integer> map = ... map.forEach((String s, Integer i) -> log.info(s + "=" + i));

Error handling

Title	默認	建議	描述
instanceof on catch parameter		warning	使用instanceof來區分異常不如使用多個catch塊
Nested try statement		warning	嵌套try

Java language level migration aids

Title	默認	建議	描述
try finally replacable with try with resources	warning	無	Before Java 7, the usual pattern was something like this: Connection con = null; PreparedStatement prep = null; try{ con = getConnection(); prep = prep.prepareStatement("Update ..."); ... con.commit(); } catch (SQLException e){ con.rollback(); throw e; } finally{ if (prep != null) prep.close(); if (con != null) con.close(); } With Java 7 you can go for: try(Connection con = getConnection(); PreparedStatement prep = con.prepareConnection("Update ..."){ ... con.commit(); }
lambda can be replaced with method reference	warning	無	不一樣風格的lambda寫法

Numberic issues

Title	默認	建議	描述
divdide by zero	warning	error	除零
equals called on java.math.BigDecimal		warning	使用compareTo

Performance

Title	默認	建議	描述
Single charactor string argument in String.indexOf call		warning	單字符串String無需indexOf直接equals便可
String.equals("")		warning	直接.length==0，可能null則使用StringUtils.isEmpty

Probable bugs

Title	默認	建議	描述
Array comparison using == instead of Array.equals		warning	正確比較數組每一個元素相等的方法Arrays.equals()
Call to default toString		warning	未覆寫ToString時使用只會打印地址
Collection added to itself	warning	無	Reports cases where the argument of a method call on a java.util.Collection or java.util.Map is the collection or map itself. This includes adding a collection to itself, which can lead to a java.lang.StackOverflowError when, for example, calling hashCode() on the self-containing collection.
equals and hashCode are not pared		warning	兩個對象若是不相等，hashCode不強制要求不同，可是若是能保證不同，對哈希的效率會比較有幫助最重要的是第二點，相等的對象必須有相同的hashCode，因爲默認的hashCode方法針對每個對象返回一個固定的隨機值（有的實現是根據對象地址返回值，至關於每個對象對應一個固定的隨機值），因此當咱們使用equals方法的同時，必須override（重寫）hashCode方法，以知足這一點。
Object comparison using == instead of equals	No high lighting,only fix	warning	比較對象相等通常不是要比較地址

Verbose or redundant code constructs

Title	默認	建議	描述
unnecessary default for enum switch statement		warning	enum case就這麼多無需default