数组隐私Java-基本

Question

I'm sorry for (another) admittedly quite basic question, but I'm having more problems in some Java code that I have to right for class. The assignment is to do a sieve of Eratosthenes program, and while my constructor seems to work (calling myArray[50] from the main method gives the value it was initialized to), it doesn't reflect any changes that the other classes were meant to make to myArray . Also, print() prints nothing (probably because the function sees an unitialized version of myArray .).

The goal is that SieveEm() and deleteStuff() mark all of the non-primes as false, the print() comes by and prints all of the prime numbers(marked true).

I couldn't seem to find anything on the internet/StackOverflow addressing the problem. What am I doing wrong?

    public class Sieve {
    private int count;
    private boolean[] myArray;
    public Sieve(int length){
        count = length+1;
        boolean[] newArray = new boolean[length+1];
        if(length>=1){
            newArray[0]=false;
            newArray[1]=false;
            if(length>=2){
                for(int i=0;i<=length;i++){
                    newArray[i]=true;
                }
            }
        }
        this.myArray = newArray;
    }
    public void SieveEm(){
        System.out.println("here now");
        System.out.println(this.myArray[50]==true);
        for(int i=0; i<count;i++){
            System.out.println("We got this far");
            if(this.myArray[i]){
                deleteStuff(i);
            }
        }
    }
    public void deleteStuff(int current){
        int increment= current;
        current+=increment;
        while(current<count){
            this.myArray[current]=false;
            current+=increment;
        }
    }
    public void print(){
        this.SieveEm();
        for(int i=2;i<count;i++){
            if(this.myArray[i]){
                System.out.println(i);
            }
        }
    }
    public static void main(String[] args){
        Sieve mySieve = new Sieve(100);
        mySieve.print();
        System.out.println(mySieve.myArray[50]);
    }
}

Answer 1

I will go method by method for anything that has issues because there seems to be a bit that needs correcting.

For public void deleteStuff(int current), this int increment= current; current+=increment; int increment= current; current+=increment; seems rather redundant and hurtful because increment does not do anything special. Even more importantly, your while - loop will never terminate because on the first pass current = 0; and increment = 0; . If you do current++; then your while-loop WILL terminate. Also, if you while loop does progress and goes through the array, all true values will be set to false.

Onto print() . This method does not print anything because you set the entire myArray to false. Of course, because of the while-loop issue I mentioned earlier, the for-loop to print is never reached because you are stuck in a never ending while-loop. So, if you solve the while - loop issue, you set every element in the array to false so the statment below never executes.

if(this.myArray[i]) { System.out.println(i); }

If I notice anything else I will let you know.