Schlagwort: Wrapper

Converting Java Collections, Array of Wrapper Types and Array of Primitives

With this post I just want to show how to convert a Java collection into an array and how to convert a wrapper class array into an array of the corresponding primitive data type. As a bonus I will show how to iterate over an ArrayList.

Code

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 public static void main(String[] args)
  {
    // Java collection (ArrayList) with Floats
    ArrayList<Float> someFloats = new ArrayList<Float>();
    someFloats.add(3.72f);
    someFloats.add(28.07f);
    someFloats.add(2011f);
    // Convert ArrayList into an array
    Float[] floatWrapperArray = someFloats.toArray(new Float[someFloats.size()]);
    float[] floatArray = new float[floatWrapperArray.length];
    // Transfer array of Wrapper type (Float) into array of primitive data type (float)
    for (int i = 0; i < floatArray.length; i++)
    {
      floatArray[i] = floatWrapperArray[i].floatValue();
    }
    // 1. Float ArrayList
    System.out.println("1. Float ArrayList");
    for (Iterator iterator = someFloats.iterator(); iterator.hasNext();)
    {
      Float currentFloat = (Float) iterator.next();
      System.out.println(currentFloat);
    }
    // 2. Float array
    System.out.println("2. Float array");
    for (int i = 0; i < floatWrapperArray.length; i++)
    {
      System.out.println(floatWrapperArray[i]);
    }
    // 3. float array
    System.out.println("3. float array");
    for (int i = 0; i < floatArray.length; i++)
    {
      System.out.println(floatArray[i]);
    }
  }

Output

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1. Float ArrayList
3.72
28.07
2011.0
2. Float array
3.72
28.07
2011.0
3. float array
3.72
28.07
2011.0