Int 数组自行排序

Question

import java.util.ArrayList;

public class Paaohjelma {
    public static int pienin(int[] taulukko) {
        int temp, size;
        size = taulukko.length;

        for(int i = 0; i<size; i++ ){
            for(int j = i+1; j<size; j++){
                if(taulukko[i]>taulukko[j]){
                    temp = taulukko[i];
                    taulukko[i] = taulukko[j];
                    taulukko[j] = temp;
                }
            }
        }
        return taulukko[0];
    }
    
    public static int pienimmanIndeksi(int[] taulukko) {
        ArrayList<Integer> tauli = new ArrayList<>();
        
        for (int i : taulukko) {
            tauli.add(i);
        }
        
        return tauli.indexOf(Paaohjelma.pienin(taulukko));
    }
    
    public static int pienimmanIndeksiAlkaen(int[] taulukko, int aloitusIndeksi) {
        // this methods should get the index of smallest value starting from specified index
        int[] tempTauli = taulukko;
        tempTauli = new int[tempTauli.length - aloitusIndeksi];
        
        // this gets the right values to temporary array
        if (aloitusIndeksi > 0) {
            int index = 0;
            int indexTauli = 0;
            for(int value : taulukko) {
                if(index >= aloitusIndeksi) {
                    tempTauli[indexTauli] = taulukko[index];
                    indexTauli++;
                }
                index++;
            }
        }
        // values added are automatically sorted from smallest to largest?
        // this shouldn't be, array should be 5, 99, 3, 12 but is shown as 3, 5, 12, 99
        for(int inty : tempTauli) {
            System.out.println(inty);
        }
        
        // get the index of smallest value in array
        // index is 0 should be 2
        int index = Paaohjelma.pienimmanIndeksi(tempTauli);
        
        // return index of smallest value (add starting index to get the index of smallest value in the original array when starting from specified index)
        return index+aloitusIndeksi;
    }
    
    public static void main(String[] args) {
        // test code
        int[] taulukko = {3, 1, 5, 99, 3, 12};
        int minIndex = Paaohjelma.pienimmanIndeksi(taulukko);
        System.out.println("Pienin: " + Paaohjelma.pienin(taulukko));
        System.out.println("Pienimmän indeksi: " + minIndex);
        System.out.println(Paaohjelma.pienimmanIndeksiAlkaen(taulukko, 2));
    }

}

Hello. I'm doing some programming course work for school and have been stuck in this particular part for couple hours. So I decided it would be best for someone else to take a look and provide some light why my approach for this problem isn't working.

What should happen: class method PienimmanIndeksiAlkaen should return the index of smallest value in provided int array starting from specified index.

The main problem I have been having is that the array seems to be automatically sorting itself and I have no idea what is possible causing this. I have commented the relevant part of the code and would be more than happy if someone could explain why this is happening and what possible could be done to prevent this.

Answer 1

The reason your array is sorted is when you call

    System.out.println("Pienin: " + Paaohjelma.pienin(taulukko));

you sort the array.

When you pass the array into this function, you aren't actually passing the value of the array, but the pointer to the array - the address of the array in memory. This is the difference between passing parameters by value or by reference .

How do you know if the value is passed by value or by reference? As a rule of thumb:

primitive values - ie int, double, etc. will be passed by value - their value will be copied and passed to the function.

Any other type, namely arrays and classes, will be passed by reference - the address of the value in memory will be passed to the function, thus any change to the value inside the function will affect it when the function ends too.

Read more here

Answer 2

import java.util.ArrayList;

public class Paaohjelma {
    public static int pienin(int[] taulukko) {
        int temp, size;
        size = taulukko.length;

        for(int i = 0; i<size; i++ ){
            for(int j = i+1; j<size; j++){
                if(taulukko[i]>taulukko[j]){
                    temp = taulukko[i];
                    taulukko[i] = taulukko[j];
                    taulukko[j] = temp;
                }
            }
        }
        return taulukko[0];
    }
    
    public static int pienimmanIndeksi(int[] taulukko) {
        ArrayList<Integer> tauli = new ArrayList<>();
        
        for (int i : taulukko) {
            tauli.add(i);
        }
        
        return tauli.indexOf(Paaohjelma.pienin(taulukko));
    }
    
    public static int pienimmanIndeksiAlkaen(int[] taulukko, int aloitusIndeksi) {
        // this methods should get the index of smallest value starting from specified index
        int[] tempTauli = taulukko;
        tempTauli = new int[tempTauli.length - aloitusIndeksi];
        
        // this gets the right values to temporary array
        if (aloitusIndeksi > 0) {
            int index = 0;
            int indexTauli = 0;
            for(int value : taulukko) {
                if(index >= aloitusIndeksi) {
                    tempTauli[indexTauli] = taulukko[index];
                    indexTauli++;
                }
                index++;
            }
        }
        // values added are automatically sorted from smallest to largest?
        // this shouldn't be, array should be 5, 99, 3, 12 but is shown as 3, 5, 12, 99
        for(int inty : tempTauli) {
            System.out.println(inty);
        }
        
        // get the index of smallest value in array
        // index is 0 should be 2
        int index = Paaohjelma.pienimmanIndeksi(tempTauli);
        
        // return index of smallest value (add starting index to get the index of smallest value in the original array when starting from specified index)
        return index+aloitusIndeksi;
    }
    
    public static void main(String[] args) {
        // test code
        int[] taulukko = {3, 1, 5, 99, 3, 12};
        int minIndex = Paaohjelma.pienimmanIndeksi(taulukko);
        System.out.println("Pienin: " + Paaohjelma.pienin(taulukko));
        System.out.println("Pienimmän indeksi: " + minIndex);
        System.out.println(Paaohjelma.pienimmanIndeksiAlkaen(taulukko, 2));
    }

}

Hello. I'm doing some programming course work for school and have been stuck in this particular part for couple hours. So I decided it would be best for someone else to take a look and provide some light why my approach for this problem isn't working.

What should happen: class method PienimmanIndeksiAlkaen should return the index of smallest value in provided int array starting from specified index.

The main problem I have been having is that the array seems to be automatically sorting itself and I have no idea what is possible causing this. I have commented the relevant part of the code and would be more than happy if someone could explain why this is happening and what possible could be done to prevent this.