Java的 @SuppressWarnings 注释

注解是Java在现代技术中非常重要的一部分，Hibernate、Spring、Spring Boot、JPA等大部分技术都在使用注解，让开发者的生活变得轻松很多。在Java，内置的通用注解是——

@覆盖
@已弃用
@功能接口
@SuppressWarnings

语法： Java @SuppressWarnings 注解的签名如下：

@Retention(value=SOURCE)
@Target(value = {TYPE, FIELD, METHOD, PARAMETER, CONSTRUCTOR, LOCAL_VARIABLE })
public @interface SuppressWarnings {
       String[] value;
    }

我们可以看到，上面的签名只有一个元素，它是字符串数组，有多个可能的值。

所有注释都有两个属性：

Target (@Target(value = {TYPE, FIELD, METHOD, PARAMETER, CONSTRUCTOR, LOCAL_VARIABLE })) – 几乎所有东西都可以使用它，无论你想抑制警告的地方。
Retention (@Retention(value=SOURCE))：功能接口“SOURCE”的保留策略，这意味着注释不会到编译器去。

插图：

使用@SuppressWarnings 是为了抑制或忽略来自编译器的警告，即编译器将忽略该代码段的警告（如果有）。

1. @SuppressWarnings("unchecked")
   public class Calculator {
          }
          
- Here, it will ignore all unchecked warnings coming from that class. (All methods, variables, constructors).

2. public class Calculator {
   @SuppressWarnings("unchecked")
      public int sum(x,y) {
        .
      }
   }
   
- It will stop warning from that function only, and not from other functions of Calculator class.

这个注解是危险的，因为警告是代码中潜在的错误。因此，如果我们收到任何警告，第一种方法应该是解决这些错误。但是如果我们要压制任何警告，我们必须有一些充分的理由。每次使用时都应该在注释附近注释原因。

@SuppressWarnings 注释元素内的可能值如下：

Values	Description
All	It will suppress all warnings.
Cast	Suppress the warning while casting from a generic type to a nonqualified type or the other way around.
Deprecation	Ignores when we’re using a deprecated(no longer important) method or type.
divzero	Suppresses division by zero warning.
empty	Ignores warning of a statement with an empty body.
unchecked	It doesn’t check if the data type is Object or primitive.
fallthrough	Ignores fall-through on switch statements usually (if “break” is missing).
hiding	It suppresses warnings relative to locals that hide variable
serial	It makes the compiler shut up about a missing serialVersionUID.
finally	Avoids warnings relative to finally block that doesn’t return.
unused	To suppress warnings relative to unused code.

Note: The primary and most important benefit of using @SuppressWarnings Annotation is that if we stuck because of some known warning, then this will ignore the warning and move ahead. E.g. – deprecated and unchecked warnings.

编程需要懂一点英语

例子：

Java

// Java Program to demonstrate Use of @SuppressWarnings
// Annotation
  
// Importing required packages
import java.io.*;
import java.lang.*;
import java.util.*;
  
// Class 1
// Helper class
class Addition {
  
    // Method 1
    public static int sum(int n1, int n2)
    {
  
        // Return the final sum
        return n1 + n2;
    }
  
    // Method 2
    public static int sum(int... nums)
    {
        int sum = 0;
        for (int i : nums) {
            sum += i;
        }
  
        // Return the final sum
        return sum;
    }
}
  
// Class 2
// Main class
// To test suppress warnings
public class GFG {
  
    // Does not check if data type is Object or primitve
    @SuppressWarnings("unchecked")
  
    // Main driver method
    public static void main(String[] args)
    {
  
        // Creating an object of above class in main()
        // method
        Addition add = new Addition();
  
        // Ignore when we're using a deprecated
        // (no longer important) method or type
        @SuppressWarnings("deprecation")
  
        int sum = Addition.sum(10, 20);
  
        // Print and display the sum
        System.out.println("Sum of 10 and 20 : " + sum);
  
        @SuppressWarnings("rawtypes")
  
        // Raw data type being used instead of generic
        List list = new ArrayList();
  
        // Custom input entries
        list.add(12);
        list.add(120);
  
        // Print and display List elements
        System.out.println("List items : " + list);
    }
}

输出

Sum of 10 and 20 : 30
List items : [12, 120]

Java的 @SuppressWarnings 注释

Values

Java