Can a Java List be output as a String?

Question

If I want to print the string "Output:" followed by whatever result a method returns, the only one that will do so on the same line as "Output:" is a method that returns a String type. For instance:

public static void main(String[] args){
  System.out.println(returnString("Hello"));
}

public static String returnString(String s){
    return "Output:" + s;
}

If, however, I want to print the string "Output:" followed by the method return of any other variable type, the return would have to be on a separate line. For instance:

public static void main(String[] args){
  System.out.println(returnInt(2));
}

 pubic static int returnInt(int n){
  System.out.println("Output:");
  return n;
}

or by changing the return type to String and using a built-in conversion method that is appropriate for the return type. For instance:

public static void main(String[] args){
  System.out.println(returnInt(2));
}

public static String returnInt(int n){
  return "Output:" + String.valueOf(n)
}

or

public static void main(String[] args){
  System.out.println(returnArray(new int[]{1, 2, 3}));
}

public static String returnArray(int[] array){
  return "Output:" + Arrays.toString(array);
}

or

public static void main(String[] args){
  System.out.println(returnBoolean(false));
}

 public static String returnBoolean(boolean b){
  return "Output:" + Boolean.toString(b);
}

So three questions:

1) It's not possible to declare two return types when initializing a method the same way you can declare two input types (i.e. methodName(int n, String S)), correct?

2) Is there any way (such as an escape sequence) that pulls the next line up ot the same line when returning a non-string?

2) And if not, is there a built-in method for returning a List (the way Arrays.toString or String.value Of do for their respective types? I can't find anything similar such as List.ToString etc.

You're misunderstanding output and the result (or return value) of a method invocation. — Sotirios Delimanolis, Feb 18 '14 at 00:37
@Ingo. thanks. that was short and sweet lol. So there's no way to allow two return types in sequence or a List conversion method like Arrays.toString, correct? — dbconfession, Feb 18 '14 at 00:41
@StuartKuredjian You can just return one value. But, of course, this value can be a tuple. — Ingo, Feb 18 '14 at 00:45
@mrres1 I think this was answered by someone else defining an object. But I was asking if its possible for one method to return say, an int and then a String. — dbconfession, Feb 18 '14 at 01:24
Nope, can't do that in Java. Check out Ruby, Python, or other languages that will pack/unpack tuples for you automatically. — Nick Veys, Feb 18 '14 at 01:29
@StuartKuredjian OK, then yes, as everyone is talking about, you are referring to a tuple. Java does not have these. http://docs.python.org/release/1.5.1p1/tut/tuples.html — mrres1, Feb 18 '14 at 02:32

score 2 · Answer 1 · edited May 23 '17 at 11:56

2

1) That's correct. A method could return an object that contained instance variables of multiple types, though.

2) If you use System.out.print() instead of System.out.println() it will not add a newline at the end.

3) This answer provides a simple way to print out the elements of a List.

System.out.println(Arrays.toString(stack.toArray()));

edited May 23 '17 at 11:56

Community

1
1

answered Feb 18 '14 at 00:43

Connor Pearson

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score 2 · Answer 2 · answered Feb 18 '14 at 00:50

2

In java you can always write the following:

Object o = someMethod();
System.out.println("Output: " + o);

The JVM will implicitly call o.toString() to convert it to a string and then append it to the string 'Output: '.

answered Feb 18 '14 at 00:50

Giovanni Botta

9,626
5
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score 1 · Answer 3 · answered Feb 18 '14 at 00:44

1) It's not possible to declare two return types when initializing a method the same way you can declare two input types (i.e. methodName(int n, String S)), correct?

Correct, in Java, if you want to return multiple things, you should make an object that represents the data you're returning, and return that. So instead of returning paws, head, body, legs and a tail object, you'd return a Dog.

2) Is there any way (such as an escape sequence) that pulls the next line up ot the same line when returning a non-string?

You bet, just don't tell it to add a newline. That's what println is doing for you, it means "print line". Instead, just use print.

2) And if not, is there a built-in method for returning a List (the way Arrays.toString or String.value Of do for their respective types? I can't find anything similar such as List.ToString etc.

Most List implementations will have a toString method, so you can definitely print them out, try it. It may not be exactly what you want, so you may have to write a helper method to format it how you're intending.

@ Nick Veys I tried that. That's what led to this whole post in the first place lol. neither List.toString() nor ArrayList.toString() work. ArrayList.toString errors with "The method toString() in the type AbstractCollection is not applicable for the arguments (List)" and using List.toString() errors with "The method toString() in the type Object is not applicable for the arguments (List)" — dbconfession, Feb 18 '14 at 01:22
Not sure exactly what you're doing wrong, but here's a simple example of printing a list: http://pastebin.com/r8CtKTy4 — Nick Veys, Feb 18 '14 at 01:27
Are you actually calling a method like `List.toString(some_list)`? Because that's not going to work. List is an interface, you can't call methods on it directly, and the `toString` is actually on the objects themselves and is called automatically when coerced into a String. — Nick Veys, Feb 18 '14 at 01:28

score 0 · Answer 4 · edited May 23 '17 at 12:03

You're going about this all wrong.

If I want to print the string "Output:" followed by whatever result a method returns, the only one that will do so on the same line as "Output:" is a method that returns a String type.

Absolutely not.

Take this method

public int returnAnInt() {
    return 42;
}

You can print the value returned by this method like so

System.out.println("Output:" + /*possibleInstance.*/returnAnInt());

This is possible due to String concatenation.

Don't write your methods with output in mind. For example, if you have a method that is supposed to calculate the sum of two integers

public int add(int a, int b) {
    return a + b;
}

Just make it calculate the sum of two integers.

There's no need to put the output in the method itself. Make the code that calls this method output the value

int sum = add(16, 27);
System.out.println("The sum is: " + sum);
// or
System.out.println("The sum is: " + add(16, 27));

As to your 3 questions, which I think become rather moot, see the other answers. You might want to look at the toString() method which all reference types inherit.

mrres1 · Answer 5 · 2014-02-18T01:03:48.943

0

public class tst
{
    public static void main(String[] args)
    {
        System.out.println(toString(1));
        System.out.println(toString("hello"));
        System.out.println(toString(false));
        System.out.println(toString(new Integer[] { 1, 2, 3 }));
    }

    static String toString(Object object)
    {
        return "Output: (" + object.getClass().getSimpleName() + ") " + object;
    }
}

The console output is:

Output: (Integer) 1
Output: (String) hello
Output: (Boolean) false
Output: (Integer[]) [Ljava.lang.Integer;@51de8adb

edited Feb 18 '14 at 01:03

answered Feb 18 '14 at 00:56

mrres1

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6
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Extremely lousy solution. – PM 77-1 Feb 18 '14 at 01:01

Can a Java List be output as a String?

5 Answers5