Print an array in Java

Write a program to print single-dimensional and multidimensional arrays in Java.

How to print 1D Arrays?

1. For-loop or Enhanced for-loop
2. Arrays class – toString() or deepToString() method
3. Apache Commons Lang – ArrayUtils.toString() method
4. Java 8 Stream
5. Arrays.asList() or Guava’s Ints.asList()

1. For-loop or Enhanced for-loop

A naive approach will be to use a for-loop, as shown below:

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We can replace the above for-loop by enhanced for-loop, as shown below:

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2. Arrays class – toString() or deepToString() method

Another simple solution would be just to use Arrays.toString(Object[] a) method that will return a string representation of the contents of the specified array. We can also use Arrays.deepToString(Object[] a) that returns a string representation of the “deep contents” of the specified array, i.e., if the array contains other arrays as elements, the string representation includes their contents and so on.

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Output:

[1, 2, 3, 4, 5]
[1, 2, 3, 4, 5]

3. Apache Commons Lang – ArrayUtils.toString() method

Arrays.toString() and Arrays.deepToString() will work only on Java SE 5 and above. Apache Commons provides ArrayUtils.toString() method, which is similar to Arrays.deepToString() and outputs an array as a String. Following are its differences with Arrays.deepToString():

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4. Java 8 Stream

In Java SE 8 and above, we can use streams to print an array. Following are the two terminal operations we can apply to a stream to print an array.

1. Get iterator to the stream Iterator itr = Arrays.stream(arr).iterator();.
2. Using Stream.forEach
   Arrays.stream(arr).forEach(System.out::println);.

The following program demonstrates it:

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5. Arrays.asList() or Guava’s Ints.asList()

For an array of non-primitive objects, we can use Arrays.asList() as shown below: Arrays.asList() returns a fixed-size list backed by the specified array. This approach is not recommended as it includes the creation of a list as an intermediate step.

Similar to Arrays.asList() method in JDK, Google’s Guava library has Ints.asList() that also returns a fixed-size list.

How to print 2D Arrays?

1. For-loop / Enhanced for-loop
2. Arrays class – toString() or deepToString() method
3. Apache Commons Lang – ArrayUtils.toString() method

1. For-loop / Enhanced for-loop

The idea is to use two for-loops – one to get the next 1D array and one to iterate through that array.

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We can also replace the above for-loop by enhanced for-loop, as shown below:

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2. Arrays class – toString() or deepToString() method

We can use Arrays.toString(Object[] a) method to print string representation of a single-dimensional array only. For multidimensional arrays, it won’t work. We know that a multidimensional array is nothing but collections of one-dimensional arrays. So, we can make Arrays.toString() work by passing each one-dimensional array to it.

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Output:

[1, 2, 3]
[1, 2, 3, 4, 5]
[1]
[1, 2]

 
Here’s an equivalent version using the Stream API.

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Output:

[1, 2, 3]
[1, 2, 3, 4, 5]
[1]
[1, 2]

3. Apache Commons Lang – ArrayUtils.toString() method

As mentioned earlier, ArrayUtils.toString() provides support for Multi-dimensional primitive and non-primitive arrays.

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Output:

{{1,2,3},{1,2,3,4,5},{1},{1,2}}

That’s all about printing an array in Java.