Using the @SafeVarargs annotation - Java Object Oriented Design

Java examples for Object Oriented Design:Generic Class

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Introduction

The @SafeVarargs and @SuppressWarnings annotations can be used to deal with various warnings that are normally harmless.

The @SafeVarargs annotation is used to designate certain methods and constructors that use a variable number of arguments as safe.

Demo Code

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

public class Main {

  public static void main(String[] args) {
    ArrayList<Integer> a1 = new ArrayList<>();
    a1.add(new Integer(1));
    a1.add(2);//from w ww  .  j a v  a 2 s  .  c  o  m
    ArrayList<Float> a2 = new ArrayList<>();
    a2.add(new Float(3.0));
    a2.add(new Float(4.0));
    displayElements(a1, a2, 12);

    // There's More: An example of heap pollution
    List<String> list1 = new ArrayList<>();
    list1.add("One");
    list1.add("Two");
    list1.add("Three");
    List<String> list2 = new ArrayList<>();
    list2.add("Four");
    list2.add("Five");
    list2.add("Six");

    merge(list1, list2);

  }

  @SafeVarargs
  public static <T> void displayElements(T... array) {
    for (T element : array) {
      System.out.println(element.getClass().getName() + ": " + element);
    }
  }

  @SafeVarargs // Not actually safe!
  static void merge(List<String>... stringLists) {
    Object[] array = stringLists;
    List<Integer> tmpList = Arrays.asList(42);
    array[0] = tmpList; // Semantically invalid, but compiles without warnings
    String element = stringLists[0].get(0); // runtime ClassCastException
  }
}

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