What is the best standard style for a toString implementation?

Question

We have a lot of objects for which we like to implement a simple toString to output attributes of the object. Some of these attributes may be complex objects themselves.

Is there any standard, or simply just a best practice for a style? I'm thinking something like:

[SimpleClassName] { prop1:value, prop2:value }

In which case a nested value would look like:

[SimpleClassName] { prop1:value, prop2:[NestedObject] { prop3:value}}

We are using Java but I find myself asking the same question in most languages!

Answer 1

json syntax seems to fit pretty well since it was designed specifically to represent complex objects as strings

Person = {
    "firstName": "John",
    "lastName": "Smith",
    "age": 25,
    "address": 
    {
        "streetAddress": "21 2nd Street",
        "city": "New York",
        "state": "NY",
        "postalCode": "10021"
    },
    "phoneNumber": 
    [
        {
            "type": "home",
            "number": "212 555-1234"
        },
        {
            "type": "fax",
            "number": "646 555-4567"
        }
    ]
}

Answer 2

If your objects have something that might be useful as an identifier, I'd implement something like your second example:

[SimpleClassName:id] { prop1:value, prop2:[NestedObject:id] { prop3:value }}

Where the id is whatever makes sense for that object to be an identifier - the name for the canonical Person object, a primary key for an object from a database, etc.

Answer 3

Personally, I find the the mix of [] and {} not so easy to get an immediate view of the hierarchy.

I like this format (and I've seen it being used in a number of places):

SimpleClassName[prop1=value, prop2=value]
SimpleClassName[prop1=value, prop2=NestedObject[prop3=value]]

There's also the possibility to add an identifier with @, for example the default style for the commons-lang ToStringBuilder does that (using it's own example):

Person@182f0db[name=John Doe,age=33,smoker=false]

Answer 4

Since you asked about what other open source projects to, here's how jEdit does it, which is similar to Wouter's:

BufferChanging[what=BUFFER_CHANGING,source=org.gjt.sp.jedit.EditPane[active,global]]

Answer 5

check out phps print_r($obj, true) or also serialize() could work, dont know exactly for what its needed for. jsons is also a clean solution, especially if u want to import the data in javascript environbments

Answer 6

I think the format produced by Guava's Objects.toStringHelper() is pretty nice, but it's mainly just good to have some consistent format that you use:

public String toString() {
  return Objects.toStringHelper(this)
      .add("prop1", prop1)
      .add("prop2", prop2)
      .toString();
}

// Produces "SimpleClassName{prop1=foo, prop2=bar}"

Answer 7

Is there any standard, or simply just a best practice for a style?

No. The "best" output for a toString() method is determined by what you want to use it for. Is it for serializing the object state in a form that allows it to be deserialized? Is it for creating debug messages? Is it for rendering the object for display to end-users?

If you want to develop an in-house style for your debug/logging toString() methods, that's fine. But unless there was a requirement for this, I wouldn't bother. IMO, it is effort that could better be spent elsewhere.