Annotation注解---详解(一)

一、Annotation概述

1.annotation其实就是代码里的特殊标记，它用于替代配置文件来告诉类如何运行。有了注解技术后，开发人员可以通过注解告诉类如何运行。

2.三个基本的Annotation

@Override:限定重写父类方法，该注解只能由于方法。可以使用此注解，来说明某个子类的方法是重写了父类方法，当父类方法中没有此方法时，将会在编译时报错。

class MyClass2 extends MyClass1{
	@Override
	public void myMethod1(){
		
	}
	
	@Override
	public void myMethod2(){
		//由于父类MyClass1没有此方法，因此在此方法上添加@Override注解将导致编译报错
	}
}

@Deprecated:用于表示某个程序元素(类，方法，属性等)已经过时，即表示将会废弃，被注解的方法将会有个删除“样式".

@Deprecated
//作用于类
class MyClass2 extends MyClass1{
	@Deprecated
	private String name; //作用于属性
	@Override
	public void myMethod1(){
		
	}
	
	@Override
	public void myMethod2(){
		//由于父类MyClass1没有此方法，因此在此方法上添加@Override注解将导致编译报错
	}
	
	@Deprecated
	public void myMethod3(){
		//作用于方法
	}
}

@SuppressWarnings：抑制编译告警

@SuppressWarnings({ "unchecked", "rawtypes" })
	public List myGetLst(){
		return null;
	}

@SuppressWarnings(option)
This can be categorized into two categories:Put this notation right before the code with warning:
@SuppressWarnings("unused") String unused = "never";
Put this notation right before the class declaration
@SuppressWarnings("deprecation")
class DeprecationExample{ ... }I think the warning options in red should be categoried into category 2.
You can simply try this out!

Warning options

-warn: allDeprecation allJavadoc assertIdentifier boxing charConcat conditionAssign constructorName dep-ann deprecation discouraged emptyBlock enumSwitch fallthrough fieldHiding finalBound finally forbidden hiding incomplete-switch indirectStatic intfAnnotation intfNonInherited javadoc localHiding maskedCatchBlocks nls noEffectAssign null over-ann paramAssign pkgDefaultMethod raw semicolon serial specialParamHiding static-access staticReceiver suppress synthetic-access syntheticAccess tasks(<task1>|...|<taskN>) typeHiding unchecked unnecessaryElse unqualified-field-access unqualifiedField unused unusedArgument unusedImport unusedLabel unusedLocal unusedPrivate unusedThrown uselessTypeCheck varargsCast warningToken

Set warning level. e.g. -warn:unusedLocal,deprecation In red are the default settings. -warn:none disable all warnings -warn:<warnings separated by ,> enable exactly the listed warnings -warn:+<warnings separated by ,> enable additional warnings -warn:-<warnings separated by ,> disable specific warnings allDeprecation deprecation even inside deprecated code allJavadoc invalid or missing javadoc assertIdentifier occurrence of assert used as identifier boxing autoboxing conversion charConcat when a char array is used in a string concatenation without being converted explicitly to a string conditionAssign possible accidental boolean assignment constructorName method with constructor name dep-ann missing @Deprecated annotation deprecation usage of deprecated type or member outside deprecated code discouraged use of types matching a discouraged access rule emptyBlock undocumented empty block enumSwitch, incomplete-switch incomplete enum switch fallthrough possible fall-through case fieldHiding field hiding another variable finalBound type parameter with final bound finally finally block not completing normally forbidden use of types matching a forbidden access rule hiding macro for fieldHiding, localHiding, typeHiding and maskedCatchBlock indirectStatic indirect reference to static member intfAnnotation annotation type used as super interface intfNonInherited interface non-inherited method compatibility javadoc invalid javadoc localHiding local variable hiding another variable maskedCatchBlocks hidden catch block nls non-nls string literals (lacking of tags //$NON-NLS-<n>) noEffectAssign assignment with no effect null missing or redundant null check over-ann missing @Override annotation paramAssign assignment to a parameter pkgDefaultMethod attempt to override package-default method raw usage a of raw type (instead of a parametrized type) semicolon unnecessary semicolon or empty statement serial missing serialVersionUID specialParamHiding constructor or setter parameter hiding another field static-access macro for indirectStatic and staticReceiver staticReceiver if a non static receiver is used to get a static field or call a static method suppress enable @SuppressWarnings syntheticAccess, synthetic-access when performing synthetic access for innerclass tasks enable support for tasks tags in source code typeHiding type parameter hiding another type unchecked unchecked type operation unnecessaryElse unnecessary else clause unqualified-field-access, unqualifiedField unqualified reference to field unused macro for unusedArgument, unusedImport, unusedLabel, unusedLocal, unusedPrivate and unusedThrown unusedArgument unused method argument unusedImport unused import reference unusedLabel unused label unusedLocal unused local variable unusedPrivate unused private member declaration unusedThrown unused declared thrown exception uselessTypeCheck unnecessary cast/instanceof operation varargsCast varargs argument need explicit cast warningToken unhandled warning token in @SuppressWarnings