How do I print actual value instead of [[Ljava.lan.Number]?

Question

I have a sample of numbers. I am storing them in a List of data points with timestamps and values. Here is my code:

List<Number> samples = {55,67,57,67};
List<Number[]> dps = Lists.newArrayList();

Calender c1; c1.set(2013, 5, 20, 15, 44, 00);

int timeStartSec = (int) (c1.getTime().getTime() / 1000);

for(Number num: samples){
    dps.add(new Number[] { timeStartSec, num});
    timeStartSec = timeStartSec+5;
}

System.out.println("Final DataPoints " + dps);

Output:

Final DataPoints [[Ljava.lang.Number;@af8358, [Ljava.lang.Number;@d80be3, [Ljava.lang.Number;@1f4689e, [Ljava.lang.Number;@1006d75, [Ljava.lang.Number;@1125127, [Ljava.lang.Number;@18dfef8, [Ljava.lang.Number;@15e83f9, [Ljava.lang.Number;@2a5330, [Ljava.lang.Number;@bb7465,]

Why is it printing as java.lang.Number instead of the appropriate value?

arshajii · Answer 1 · 2013-06-24T19:37:01.603

9

Arrays don't override the toString method (annoyingly). Have a look at Arrays.toString.

Number[] nums = {1, 2, 3, 4};
System.out.println(nums);
System.out.println(Arrays.toString(nums));

[Ljava.lang.Number;@14b7453
[1, 2, 3, 4]

In your case, you will want to call Arrays.toString on each element of dps, printing / storing the results.

edited Jun 24 '13 at 19:37

answered Jun 24 '13 at 19:29

arshajii

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Interesting nuance about arrays that I wasn't unaware of. – AndyPerfect Jun 24 '13 at 19:33

score 1 · Answer 2 · answered Jun 24 '13 at 19:31

1

instance of Array does not have the toString() method. You may want to use ArrayList instead:

List<Number> samples - {55,67,57,67};
List<List<Number>> dps = new ArrayList<List<Number>>();

for(Number num: samples){

    dps.add(Arrays.asList(timeStartSec, 10));
    timeStartSec = timeStartSec+5;
}
System.out.println("Final DataPoints " + dps);

EDIT: or the static method defined on the class Arrays: Arrays.toString()

answered Jun 24 '13 at 19:31

Jiri Kremser

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Using ArrayList instead of Arrays worked. Thanks – user2325703 Jun 24 '13 at 19:36
Changing something fundamental like that (array to list) just for the sake of `toString` seems drastic. – arshajii Jun 24 '13 at 19:49
I don't like combining `Collections` and `Arrays` it is pretty unnatural. I would go either with `Number[][]` or `List>` – Jiri Kremser Jun 24 '13 at 19:51

How do I print actual value instead of [[Ljava.lan.Number]?

2 Answers2