String[] arr = {"123", "345", "437", "894"};
int[] nums = new int[arr.length];

for (int i = 0; i < arr.length; i++) {
nums[i]=Integer.parseInt(arr[i]);
}

int min = nums[0];
int max = nums[0];

for (int num: nums) {
if(min > num)
min = num;
else if(max < num)
max = num;
}

System.out.println("Min: "+min);
System.out.println("Max: "+max);
System.out.println("Toplam: "+(min+max));