Java知识点总结（注解-内置注解）

@(Java知识点总结)[Java, 注解]

@override

• 定义在java.lang.Override 中，此注释只适用于修饰方法，表示一个方法声明打算重写父类的另一个方法声明。

public class Demo01 {      @Override   public String toString() {     return "";   }   }

源码

 import java.lang.annotation.*;   /**  * Indicates that a method declaration is intended to override a  * method declaration in a supertype. If a method is annotated with  * this annotation type compilers are required to generate an error  * message unless at least one of the following conditions hold:  *  * <ul><li>  * The method does override or implement a method declared in a  * supertype.  * </li><li>  * The method has a signature that is override-equivalent to that of  * any public method declared in {@linkplain Object}.  * </li></ul>  *  * @author  Peter von der Ah&eacute;  * @author  Joshua Bloch  * @jls 9.6.1.4 @Override  * @since 1.5  */ @Target(ElementType.METHOD) @Retention(RetentionPolicy.SOURCE) public @interface Override { }

@DePRecated

• 定义在java.lang.Deprecated中，遗弃、废弃，不建议使用。此注释可用于修饰方法、属性、类，表示不鼓励程序员使用这样的元素，通常是因为它很危险或存在更好的选择。

public class Demo01 {   @Deprecated   public static void test1(){       }       public static void main(String[] args) {    test1();   } }

源码

import java.lang.annotation.*; import static java.lang.annotation.ElementType.*;   /**  * A program element annotated @Deprecated is one that programmers  * are discouraged From using, typically because it is dangerous,  * or because a better alternative exists.  Compilers warn when a  * deprecated program element is used or overridden in non-deprecated code.  *  * @author  Neal Gafter  * @since 1.5  * @jls 9.6.3.6 @Deprecated  */ @Documented @Retention(RetentionPolicy.RUNTIME) @Target(value={CONSTRUCTOR, FIELD, LOCAL_VARIABLE, METHOD, PACKAGE, PARAMETER, TYPE}) public @interface Deprecated { }

@SupPressWarings

• 定义在java.lang.SuppressWarnings中，用来抑制编译时的警告信息。
• 与前两个注释有所不同， 你需要添加一个参数才能正确使用 ，这些参数值是已经定义好了的，我们选择性的使用就好了，参数如下：

@SuppressWarnings("unchecked") @SuppressWarnings(value={"unchecked","deprecation"})

import java.util.ArrayList; import java.util.List;   public class Demo01 {   @SuppressWarnings("all")   public static void test2(){    List list = new ArrayList();  }

源码

package java.lang;   import java.lang.annotation.*; import static java.lang.annotation.ElementType.*;   /**  * Indicates that the named compiler warnings should be suppressed in the  * annotated element (and in all program elements contained in the annotated  * element).  Note that the set of warnings suppressed in a given element is  * a superset of the warnings suppressed in all containing elements.  For  * example, if you annotate a class to suppress one warning and annotate a  * method to suppress another, both warnings will be suppressed in the method.  *  * <p>As a matter of style, programmers should always use this annotation  * on the most deeply nested element where it is effective.  If you want to  * suppress a warning in a particular method, you should annotate that  * method rather than its class.  *  * @author Josh Bloch  * @since 1.5  * @jls 4.8 Raw Types  * @jls 4.12.2 Variables of Reference Type  * @jls 5.1.9 Unchecked Conversion  * @jls 5.5.2 Checked Casts and Unchecked Casts  * @jls 9.6.3.5 @SuppressWarnings  */ @Target({TYPE, FIELD, METHOD, PARAMETER, CONSTRUCTOR, LOCAL_VARIABLE}) @Retention(RetentionPolicy.SOURCE) public @interface SuppressWarnings {     /**      * The set of warnings that are to be suppressed by the compiler in the      * annotated element.  Duplicate names are permitted.  The second and      * successive occurrences of a name are ignored.  The presence of      * unrecognized warning names is <i>not</i> an error: Compilers must      * ignore any warning names they do not recognize.  They are, however,      * free to emit a warning if an annotation contains an unrecognized      * warning name.      *      * <p> The string {@code "unchecked"} is used to suppress      * unchecked warnings. Compiler vendors should document the      * additional warning names they support in conjunction with this      * annotation type. They are encouraged to cooperate to ensure      * that the same names work across multiple compilers.      * @return the set of warnings to be suppressed      */     String[] value(); }