印刷阵列法

Question

I am trying to print out my methods calSum and calMean. I want to get a similar output to:

java RandomArray 8

0 9 5 3 5 6 0 8

Sum: 36

Mean: 4.5

but instead I am getting - Usage: java RandomArray . Example: java RandomArray 5

Am I doing something wrong in the printArray method? Or is it something else? Any help with the errors in my code would be great.

    public class RandomArray {

private int[] numbers; //instance variable

/**
 *  Constructor
 *
 *The size of the array
 */
public RandomArray(int size){
    numbers = new int[size];
    for(int i=0; i<numbers.length;i++){
        numbers[i] = (int)(Math.random()*10); // a random number between 0-9
    }
}

/**
 *  a method to print the array elements
 */

public void printArray() {
    for (int i = 0; i < numbers.length; i++)
        System.out.print("Java Random array:"+ numbers);
        System.out.println("Sum:" + calSum());
        System.out.println("Mean:" + calMean());
}       

/**
 *  A method to calculate the sum of all elements
 *
 */
public int calSum(){
 int sum = 0;
 for (int value : numbers) {
     sum += value;
}
    return sum;

}

/**
 *  A method to calculate the mean of all elements
 *
 *@return    The mean
 */

public double calMean() {
    int sum = calSum();
    int length = numbers.length;

    return (double) sum / length;
}


/**
 *  a method to print the array elements in reverse order
 */
public void printReverse(){


}

/**
 *  A main method to test
 */
public static void main(String[] args) {
    // Check to see if the user has actually sent a paramter to the method
    if (args.length != 1){
        System.out.println("Usage: java RandomArray <NUM>. Example: java RandomArray 5");
        System.exit(-1);
    }

    // Create an instance of the class 
    RandomArray test = new RandomArray(Integer.parseInt(args[0]));


    // Print the array
    test.printArray();

    // Calculate the sum of all the values in the array and print it
    System.out.println("Sum: "+ test.calSum());

    // Calculate the mean of all the values in the array and print it
    System.out.println("Mean: "+ test.calMean());

    System.out.print("Reverse: ");
    test.printReverse();
}

 }

Answer 1

When you run the main class, the main method accepts an array of elements of type String .

You have to keep in mind the call looks like java RandomArray arg1 arg2 , even when you run it within an IDE. The array include all elements after java, even RandomArray .

So args will always be made of at least 1 element. If you want the value arg1 , you need to get args[1] not args[0] .

Your code should looks like:

public static void main(String[] args) {
    // Check to see if the user has actually sent a paramter to the method
    if (args.length != 2){
        System.out.println("Usage: java RandomArray <NUM>. Example: java RandomArray 5");
        System.exit(-1);
    }

    // Create an instance of the class 
    RandomArray test = new RandomArray(Integer.parseInt(args[1]));

...

Next, you won't get the expected result when printing the generate array. Check the link in the comments to see how to properly print an array.