"" + someInt; Integer.parseInt(str)

Week 3: Objects, files and exceptions/7. Convert to a number list

@@ -0,0 +1,120 @@
+Write the method
+
+ArrayList<Integer> numList(ArrayList<String> list)
+
+which takes a list of strings as its parameter.
+Strings containing numbers.
+
+The method returns a new list of integer type, with the contents of the strings converted to integers.
+
+
+Example method call:
+public static void main(String[] parameters){
+    ArrayList<String> list = new ArrayList<>();
+    list.add("2");
+    list.add("10");
+    list.add("-999");
+
+    System.out.println(numList(list));
+}
+Program outputs:
+[2, 10, -999]
+
+
+==========================================
+
+
+
+import java.util.Random;
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.stream.Collectors;
+
+public class Test{
+    public static void main(String[] args){
+        final Random r = new Random();
+        
+        testaa(new int[]{4,20,3,6,7,8,9,11});
+        testaa(new int[]{1,5,2,4,3,6,4,7,5,8,6,3,9,5,3});
+        testaa(new int[]{-5,-4,-1,-2,-3,-6,-7});
+        
+        int pituus = r.nextInt(10) + 10;
+        int[] l = new int[pituus];
+        for (int i=0; i<pituus; i++) {
+            l[i] = (100 - r.nextInt(200));
+        }
+        testaa(l);
+        
+        
+    }
+    
+    // testaa used by main
+    public static void testaa(int[] l) {
+        ArrayList<String> lista = new ArrayList<>();
+        
+        // convert from int to string element
+        for (int a : l) {
+            lista.add("" + a);
+        }
+        System.out.println("Testing with list ");
+        System.out.print("");
+        tulosta(lista);
+
+        // convert BACK from string to integer element
+        System.out.println("As integers: " + numList(lista));
+        System.out.println("");
+    }
+    
+    // tulosta used by testaa
+    public static void tulosta(ArrayList<String> lista) {
+        System.out.print("[\"");
+        // so the joined string becomes
+        // [" from above
+        // 1", "2", "3
+        // ", " is the 'delimiter'
+        // "] from below
+        System.out.print(String.join("\", \"", lista));
+        System.out.println("\"]");
+    }
+    
+
+
+
+    // numList used by testaa
+    public static ArrayList<Integer> numList(ArrayList<String> list) {
+        ArrayList<Integer> list2 = new ArrayList<>();
+        // convert string to integer element
+        // https://www.geeksforgeeks.org/java/integer-valueof-vs-integer-parseint-with-examples/
+        for (String s : list) {
+            list2.add(Integer.parseInt(s));
+        }
+        return list2;
+    }
+
+
+
+
+
+}
+
+
+
+
+
+Testing with list 
+["4", "20", "3", "6", "7", "8", "9", "11"]
+As integers: [4, 20, 3, 6, 7, 8, 9, 11]
+
+Testing with list 
+["1", "5", "2", "4", "3", "6", "4", "7", "5", "8", "6", "3", "9", "5", "3"]
+As integers: [1, 5, 2, 4, 3, 6, 4, 7, 5, 8, 6, 3, 9, 5, 3]
+
+Testing with list 
+["-5", "-4", "-1", "-2", "-3", "-6", "-7"]
+As integers: [-5, -4, -1, -2, -3, -6, -7]
+
+Testing with list 
+["-30", "27", "-21", "-93", "-24", "-4", "-26", "66", "82", "-14", "-60", "88", "-94", "10", "-49", "58", "-49", "-75"]
+As integers: [-30, 27, -21, -93, -24, -4, -26, 66, 82, -14, -60, 88, -94, 10, -49, 58, -49, -75]
+
+