Java: print_r?

Question

Hi guys,

last time I asked how to populate a data structure here. Now I would like to know if there's something in Java, like the print_r I use in PHP, to represent what I have populated in the Maps and lists without having to do my own algorithm.

Any ideas?

Answer 1

Calling toString on the collection should return a string containing all the elements string representations.

This won't work with built-in arrays though, as they don't have a toString override and will just give you a memory address.

Answer 2

I don't know of an equivalent of print_r in java.

But...

Every object has a default implementation of the toString() method, the list and map implementations print their contents if you call toString() for them.

If you need any debug information printed out, toString() may be the place you are looking for.

Answer 3

You might try the good old Apache Commons Lang's ToStringBuilder.

Answer 4

There is no equivalent for print_r in Java.

But for maps or lists you can use the foreach-loop like this:

List <String> list = …; // fills your list 

// print each list element 

for (String s : list) {

   System.out.println(s);

 }

Answer 5

For arrays the easiest way is Arrays.asList(array).toString() . I generally implement toString() on objects I like to habe in debug outputs. For generated objects (JAXB etc.) though might need to make an utility class to print it.

Answer 6

Others have mentioned the toString() method. This is really only useful when the object implements toString(). If it has not been implemented properly you will end up with something like this: java.lang.Object@1b9240e. Even if it is a little tedious it is still easy to implement toString() in your own classes, but third party classes will not always implement it. You are much better off using a debugger. The only reason things like print_r even exist in PHP is because of the lack of a real debugger. I think you will find that being able to set breakpoints instead of using a bunch of diagnostic print statements will result in a much faster workflow and cleaner code.

Answer 7

Depending on exactly what you want to do, the solution could be fairly simple. The following won't produce the formatted output that print_r provides, but it will allow you to output the structure of lists, arrays, and maps:

    // Output a list
    final List<String> list = new ArrayList<String>();
    list.add("one");
    list.add("two");
    list.add("three");
    list.add("four");
    System.out.println(list);

    // Output an array
    final String[] array = {"four", "three", "two", "one"};
    System.out.println(Arrays.asList(array));

    // Output a map
    final Map<String, String> map = new HashMap<String, String>();
    map.put("one", "value");
    map.put("two", "value");
    map.put("three", "value");
    System.out.println(map.entrySet());

For other types of objects you could use reflection to create a utility for this purpose.