此答案基于问题评论。

import java.util.Random;

import java.lang.Math; 

import java.util.Scanner;

public class Main

{

    public static void main(String[] args)

    {    

        Random rand = new Random(); //opening Random function;
        int randomNumber; //variable to store random numbers before assigning to the array
        int bonusGameNumber[]=new int [5]; //array for storing bonus game numbers
        int bonusGameWinningNumber=0;

        System.out.println("Possible winnings: €10,€20,€50,€200 and €1000. Good luck!");
        for (int m=1; m<=4; m++) // loop generating numbers for bonus game
        {
            randomNumber = rand.nextInt(999)+1;
            if (randomNumber <=600)
            {
                System.out.println("€10");
                bonusGameNumber[m] = 1;
            } else if (randomNumber >600 && randomNumber <800)
            {
                System.out.println("€20");
                bonusGameNumber[m] = 2;
            }else if (randomNumber >800 && randomNumber <900)
            {
                System.out.println("€50");
                bonusGameNumber[m] = 3;
            }else if (randomNumber >900 && randomNumber <975)
            {
                System.out.println("€200");
                bonusGameNumber[m] = 4;
            }else if (randomNumber >975 && randomNumber <=1000)
            {
                System.out.println("€1000");
                bonusGameNumber[m] = randomNumber;
            } 

        }
        for (int z=1; z<=4; z++) // loop to make sure numbers have been assigned propely.
        {
            System.out.println(bonusGameNumber[z]);
        }
        for (int n=1;n<=4;n++) //loop checking if any number got doubled,if so,assigning higher value to variable "bonusGameWinningNumber" (which has default value of 0)
        {
            for (int o=1; o<=4; o++)
            {
                if (n != o) 
                {
                    if (bonusGameNumber[n] == bonusGameNumber[o])  
                    {
                        if(bonusGameWinningNumber < bonusGameNumber[o]) 
                        {
                            bonusGameWinningNumber = bonusGameNumber[0];
                            System.out.println("test");
                        }
                    }                   
                }
            }
        }
        System.out.println(bonusGameWinningNumber); //testing if any number got assigned to the variable,it never does...

        switch(bonusGameWinningNumber) {
        case 1:
            System.out.println("Congratulations,you won €10 in the bonus game");
            break;
        case 2:
            System.out.println("Congratulations,you won €20 in the bonus game");
            break;
        case 3:
            System.out.println("Congratulations,you won €50 in the bonus game");
            break;
        case 4:
            System.out.println("Congratulations,you won €200 in the bonus game");
            break;
        case 5:
            System.out.println("Congratulations,you won €1000 in the bonus game");
            break;
        default:
            System.out.println("Sorry,you didn't win anything in the bonus game. Better luck next time!");
        }
    }
}