CODEWITHSUNDEEP
javaarrays
Zhdanovas Valerka
Zhdanovas Valerka

Reputation: 17

Print the array which size should be providedd in the command line

Declare array m of integer values and create it (allocate memory). The size of the array should be defined by the parameter provided in the command line during program execution. 

public class A {
    public static void main(String[] args) {

        int[] a;
        int[] b = new int[n];
        for (int i = 0; i < n; i++) {
            b[i] = a[i];
        }
    }
}

This is my code but I think it's incorrect. Should I use a variable args in my code? And please explain me more about memory allocation. Thank you.

Upvotes: 0

Views: 81

Answers (4)

user unknown
user unknown

Reputation: 36229

It's not clear, whether you need Scanner on Inputstream or something similar, or whether you can use the args:

The size of the array should be defined by the parameter provided in the command line during program execution.

"Parameter" sounds much like args, but they are provided ahead of program execution, not during.

But during program execution, I wouldn't call it a parameter, but an input.

Since you don't need any imports, using args is less complex.

Upvotes: 0

MC Emperor
MC Emperor

Reputation: 22977

You indeed need to use the args variable. Parameters you pass to the Java program are stored into the args variable by the JVM, making them available for the programmer.

I assume one parameter (the intended array size) is passed to the program, and that will be args[0].

You need to parse this String as an int, and use that number as array size:

// We assume args[0] exists and can be parsed as an integer, or else a
// NumberFormatException will be thrown
int size = Integer.valueOf(args[0]);

// We can use the size variable as array size.
int[] m = new int[size];

Now the array m has a size of the number given through the command line. Notice that the array size is not known at compile time, only at runtime. An array cannot be resized once created. Its length can be retrieved using m.length. Its values are initialized to 0.

If you want to print each element of the array, you can use

  • a for loop:

    for (int i = 0; i < m.length; i++) { // Loop variables are often called i
    // System.out.println prints its argument to the console
    System.out.println(m[i]);
}

  • or an enhanced for loop (also known as a foreach loop):

    for (int n : m) {
    System.out.pritnln(n);
}

  • or using Java Streams:

    either

    Arrays.stream(m).forEach(System.out::println);

    or

    IntStream.of(m).forEach(System.out::println);

More about memory allocation:

Upvotes: 1

Maniche
Maniche

Reputation: 19

Yes, you should use variable args in your code.

Parse String args to number:

int firstArg;
if (args.length > 0) {
    try {
        firstArg = Integer.parseInt(args[0]);
    } catch (NumberFormatException e) {
        System.err.println("Argument" + args[0] + " must be an integer.");
        System.exit(1);
    }
}

Refer: https://docs.oracle.com/javase/tutorial/essential/environment/cmdLineArgs.html

Upvotes: 1

Akila Sachitra
Akila Sachitra

Reputation: 1260

1) you need initialize a[]

2) use String[] args to retrieve command line argument (and you need to parse it to Integer )

Try like this .

class A {
  public static void main(String[] args) {
    try {
      String nn = args[0];
      int n = Integer.parseInt(nn);

      int[] a = new int[n];
      for (int i = 0; i < n; i++) {
        // your implementation goes here
      }
    }
    catch (ArrayIndexOutOfBoundsException e) {
      System.out.println("Please specify a argument");
    }
    catch (NumberFormatException e) {
      System.out.println("Argument must be a integer value");
    }
  }
}

Upvotes: 1

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