Question

I am working on a tool that writes java files. At a given point I have to write an array declaration. I have implemented the following methods:

  public static String arrayToCode(Long[] arr, String arrName) {
    StringBuilder sb = new StringBuilder();

    sb.append("Long[]" + arrName + " = { ");
    for (int i = 0; i < arr.length; i++) {
      sb.append(arr[i] + "L, ");
    }
    sb.append("};");

    return sb.toString();
  }

  public static String arrayToCode(String[] arr, String arrName) {
    StringBuilder sb = new StringBuilder();

    sb.append("String[]" + arrName + " = { ");
    for (int i = 0; i < arr.length; i++) {
      sb.append(arr[i] + "L, ");
    }
    sb.append("};");

    return sb.toString();
  }

  public static String arrayToCode(Double[] arr, String arrName) {
    StringBuilder sb = new StringBuilder();

    sb.append("Double[]" + arrName + " = { ");
    for (int i = 0; i < arr.length; i++) {
      sb.append(arr[i] + "L, ");
    }
    sb.append("};");

    return sb.toString();
  }

However, I would like to make a single and generic method for all sorts of arrays, the thing is that I don’t know how to handle the type with generics, i.e. how would I know it is a Long, String or Double array?

Answer 1

You can accept an Object[] and then use getClass() to figure out what type it really is.

public static String arrayToCode(Object[]  arr, String arrName) {
    String arrayTypeText = getArrayType(arr);
    sb.append(arrayTypeText + " " + arrName + ...);
    //...
}


private String getArrayType(Object[] arr) {
    Class<?> clazz = arr.getClass();
    if ( clazz == Double[].class ) {
        return "Double[]";
    } else if (...) {
    }
}

An alternative implementation of getArrayType() might be

private String getArrayType(Object[] arr) {
    return arr.getClass().getComponentType().getSimpleName() + "[]";
}

If you’re really trying to generate code you probably should just use the fully qualified name, in which case you can replace getSimpleName() above with getName() (which will return java.lang.Long, e.g.)