What's the simplest way to print a Java array?
What's the simplest way to print a Java array?
Question
In Java, arrays don't override toString(), so if you try to print one directly, you get the className + '@' + the hex of the hashCode of the array, as defined by Object.toString():
int[] intArray = new int[] {1, 2, 3, 4, 5};
System.out.println(intArray); // prints something like '[[email protected]'
But usually, we'd actually want something more like [1, 2, 3, 4, 5]. What's the simplest way of doing that? Here are some example inputs and outputs:
// Array of primitives:
int[] intArray = new int[] {1, 2, 3, 4, 5};
//output: [1, 2, 3, 4, 5]
// Array of object references:
String[] strArray = new String[] {"John", "Mary", "Bob"};
//output: [John, Mary, Bob]
Accepted Answer
Since Java 5 you can use Arrays.toString(arr) or Arrays.deepToString(arr) for arrays within arrays. Note that the Object[] version calls .toString() on each object in the array. The output is even decorated in the exact way you're asking.
Examples:
Simple Array:
String[] array = new String[] {"John", "Mary", "Bob"}; System.out.println(Arrays.toString(array));Output:
[John, Mary, Bob]Nested Array:
String[][] deepArray = new String[][] {{"John", "Mary"}, {"Alice", "Bob"}}; System.out.println(Arrays.toString(deepArray)); //output: [[Ljava.lang.String;@106d69c, [Ljava.lang.String;@52e922] System.out.println(Arrays.deepToString(deepArray));Output:
[[John, Mary], [Alice, Bob]]doubleArray:double[] doubleArray = { 7.0, 9.0, 5.0, 1.0, 3.0 }; System.out.println(Arrays.toString(doubleArray));Output:
[7.0, 9.0, 5.0, 1.0, 3.0 ]intArray:int[] intArray = { 7, 9, 5, 1, 3 }; System.out.println(Arrays.toString(intArray));Output:
[7, 9, 5, 1, 3 ]
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Always check the standard libraries first.
import java.util.Arrays;
Then try:
System.out.println(Arrays.toString(array));
or if your array contains other arrays as elements:
System.out.println(Arrays.deepToString(array));
This is nice to know, however, as for "always check the standard libraries first" I'd never have stumbled upon the trick of Arrays.toString( myarray )
--since I was concentrating on the type of myarray to see how to do this. I didn't want to have to iterate through the thing: I wanted an easy call to make it come out similar to what I see in the Eclipse debugger and myarray.toString() just wasn't doing it.
import java.util.Arrays;
.
.
.
System.out.println( Arrays.toString( myarray ) );
In JDK1.8 you can use aggregate operations and a lambda expression:
String[] strArray = new String[] {"John", "Mary", "Bob"};
// #1
Arrays.asList(strArray).stream().forEach(s -> System.out.println(s));
// #2
Stream.of(strArray).forEach(System.out::println);
// #3
Arrays.stream(strArray).forEach(System.out::println);
/* output:
John
Mary
Bob
*/
Starting with Java 8, one could also take advantage of the join() method provided by the String class to print out array elements, without the brackets, and separated by a delimiter of choice (which is the space character for the example shown below):
String[] greeting = {"Hey", "there", "amigo!"};
String delimiter = " ";
String.join(delimiter, greeting)
The output will be "Hey there amigo!".
If you're using Java 1.4, you can instead do:
System.out.println(Arrays.asList(array));
(This works in 1.5+ too, of course.)