ArrayList<Integer> lista = new ArrayList<>(); for (int l : pa) lista.add(l);

Week 3: Objects, files and exceptions/3b. Add sum to list - RECREATE LIST

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+Write the method
+
+void addSum(ArrayList<Integer> numbers) 
+
+...which calculates the sum of the numbers in the list and adds it as the last element of the list.
+
+
+Example method call:
+public static void main(String[] parameters){
+    ArrayList<Integer> numbers = new ArrayList<>();
+    for (int i=1; i<5; i++) {
+        numbers.add(i);
+    }
+    System.out.println(numbers);
+    addSum(numbers);
+    System.out.println(numbers);
+}
+
+Program outputs:
+[1, 2, 3, 4]
+[1, 2, 3, 4, 10]
+ 
+ 
+===============================================
+ 
+import java.util.Random;
+import java.util.ArrayList;
+
+public class Test{
+    public static void main(String[] args){
+        final Random r = new Random();
+        
+        int[][] s = {{1,2,3}, {10,20,30,40}, {2,4,6,8,10}, {9,1,8,2,7,3,6,4}};
+        
+        for (int[] pa : s) {
+
+            // if we do not recreate a new list
+            // then go through each element to add then to our new list
+            // we get the references
+            // [I@29ba4338
+            // [I@57175e74
+            // [I@7bb58ca3
+            // [I@c540f5a
+            ArrayList<Integer> lista = new ArrayList<>();
+            for (int l : pa) lista.add(l);
+            // vs recreating a new list for each sub-list
+            // [1, 2, 3]
+            // [10, 20, 30, 40]
+            // [2, 4, 6, 8, 10]
+            // [9, 1, 8, 2, 7, 3, 6, 4]
+            
+            
+            System.out.println("List before: ");
+            System.out.println("" + lista);
+            System.out.println("List after: ");
+            addSum(lista);
+            System.out.println(lista);
+        }
+    }
+
+
+    //ADD
+    // dont return anything
+    // cuz we update the list inplace
+    public static void addSum(ArrayList<Integer> numbers) {
+        int sum = 0;
+        for (int i : numbers) {
+            sum += i;
+        }
+        numbers.add(sum);
+    }
+
+
+
+
+}
+
+
+
+
+
+
+
+
+
+List before: 
+[1, 2, 3]
+List after: 
+[1, 2, 3, 6]
+List before: 
+[10, 20, 30, 40]
+List after: 
+[10, 20, 30, 40, 100]
+List before: 
+[2, 4, 6, 8, 10]
+List after: 
+[2, 4, 6, 8, 10, 30]
+List before: 
+[9, 1, 8, 2, 7, 3, 6, 4]
+List after: 
+[9, 1, 8, 2, 7, 3, 6, 4, 40]
+
+
+
+