如何计算字符串中的数字

Question

The code is close to correct, but I cannot see how I can move from System.out.println to a toString() method here, what am I missing?

import java.util.Scanner;

class Histogram
{
    private int[] numCount;
    int size=0;

    public Histogram(String line)
    { 
        setList(line);
    }

    public void setList(String line)
    {
        numCount = new int[20];

        for(int i=0;i<10;i++)
            numCount[i]=0;

        Scanner chopper = new Scanner (line);
        while (chopper.hasNextInt())
        {
            int num = chopper.nextInt();
            numCount[num]++;
        }

        for(int i=0;i<10;i++)
            System.out.println(i+"::"+numCount[i]);

        System.out.println();
        System.out.println();
    }
}

Answer 1

First, in setList() the default value of the primitive int is 0. And if you're using decimal math you only need 10 digits. And remove the println (s);

public void setList(String line) {
    numCount = new int[10]; // <-- base 10
    Scanner chopper = new Scanner(line);
    while (chopper.hasNextInt()) {
        int num = chopper.nextInt();
        numCount[num]++;
    }
    // once the loop is done, you can do
    System.out.println(this); // <-- will call toString so
}

Next override toString() . You might use Arrays.toString(int[]) which Returns a string representation of the contents of the specified array like

@Override
public String toString() {
    return Arrays.toString(numCount);
}

Finally, I personally would have preferred an implementation of setList(String) like

private int[] numCount = new int[10]; // <-- base 10

public void setList(String line) {
    for (char ch : line.toCharArray()) {
        numCount[Character.digit(ch, 10)]++;
    }
}