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 {@Overridepublic 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 {@Deprecatedpublic 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();
}