注解用法详解——@SuppressWarnings

一、前言

编码时我们总会发现如下变量未被使用的警告提示：

上述代码编译通过且可以运行，但每行前面的“感叹号”就严重阻碍了我们判断该行是否设置的断点了。这时我们可以在方法前添加 @SuppressWarnings(“unused”) 去除这些“感叹号”。

二、 @SuppressWarings注解

作用：用于抑制编译器产生警告信息。

示例1——抑制单类型的警告：

@SuppressWarnings(“unchecked”)
public void addItems(String item){
@SuppressWarnings(“rawtypes”)
List items = new ArrayList();
items.add(item);
}
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示例2——抑制多类型的警告：

@SuppressWarnings(value={“unchecked”, “rawtypes”})
public void addItems(String item){
List items = new ArrayList();
items.add(item);
}
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示例3——抑制所有类型的警告：

@SuppressWarnings(“all”)
public void addItems(String item){
List items = new ArrayList();
items.add(item);
}
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三、注解目标

通过 @SuppressWarnings 的源码可知，其注解目标为类、字段、函数、函数入参、构造函数和函数的局部变量。

而家建议注解应声明在最接近警告发生的位置。

四、抑制警告的关键字

关键字

用途

all

to suppress all warnings

boxing

to suppress warnings relative to boxing/unboxing operations

cast

to suppress warnings relative to cast operations

dep-ann

to suppress warnings relative to deprecated annotation

deprecation

to suppress warnings relative to deprecation

fallthrough

to suppress warnings relative to missing breaks in switch statements

finally

to suppress warnings relative to finally block that don’t return

hiding

to suppress warnings relative to locals that hide variable

incomplete-switch

to suppress warnings relative to missing entries in a switch statement (enum case)

nls

to suppress warnings relative to non-nls string literals

null

to suppress warnings relative to null analysis

rawtypes

to suppress warnings relative to un-specific types when using generics on class params

restriction

to suppress warnings relative to usage of discouraged or forbidden references

serial

to suppress warnings relative to missing serialVersionUID field for a serializable class

static-access

o suppress warnings relative to incorrect static access

synthetic-access

to suppress warnings relative to unoptimized access from inner classes

unchecked

to suppress warnings relative to unchecked operations

unqualified-field-access

to suppress warnings relative to field access unqualified

unused

to suppress warnings relative to unused code