Why do I need to use @SafeVarargs in Java 9?-javaTutorial-php.cn

Why do I need to use @SafeVarargs in Java 9?

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Release： 2023-09-11 23:53:02

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为什么在Java 9中需要使用@SafeVarargs？

The varargs feature has been introduced in Java to facilitate the creation of methods with a variable number of parameters without resorting to array types Parameters or overloaded versions of the same method.

Prior to Java 9 versions, there was a warning message if the vararg method was used with generics. Although not all methods produce heap pollution, the compiler displays a warning for all variadic methods used with generics. That's why the @SafeVarargs concept was added in Java 9 version to avoid these warnings. If we add this annotation, the compiler will stop these warnings.

We can use the following command to compile the code

<strong>javac -Xlint:unchecked SafeVarargsTest1.java</strong>

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In the example below, the compiler displays a warning message to the user.

Example

import java.util.Arrays;
import java.util.List;

public class SafeVarargsTest1 {
   public static void main(String args[]) {
      SafeVarargsTest1 test = new SafeVarargsTest1();
      test.<strong>varargsMethod</strong>(<strong>Arrays.asList</strong>("Adithya", "Jaidev"), Arrays.asList("Raja", "Chaitanya"));
   }
   private void varargsMethod(<strong>List<String></strong>... list) {
      for(List list1: list)
         System.out.println(list1);
   }
}

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Output

<strong>SafeVarargsTest.java:7: warning: [unchecked] unchecked generic array creation for varargs parameter of type List[]
test.varargsMethod(Arrays.asList("Adithya", "Jaidev"), Arrays.asList("Raja", "Chaitanya"));
^
SafeVarargsTest.java:9: warning: [unchecked] Possible heap pollution from parameterized vararg type List
private void varargsMethod(List... list) {
^
2 warnings</strong>

<strong>[Adithya, Jaidev]
[Raja, Chaitanya]</strong>

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##In the example below, we applied @ SafeVarargsbefore private methods. Therefore, it does not display any warning message.

Example
import java.util.Arrays; import java.util.List; public class SafeVarargsTest2 { public static void main(String args[]) { SafeVarargsTest2 test = new SafeVarargsTest2(); test.varargsMethod(Arrays.asList("Adithya", "Jaidev"), Arrays.asList("Raja", "Chaitanya")); } @SafeVarargs private void varargsMethod(List<String>... list) { for(List list1: list) System.out.println(list1); } }
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Output
[Adithya, Jaidev] [Raja, Chaitanya]
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