Traversing ArrayLists Practice

Sample questions

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1. Sample 1difficulty 2/5

   public static int sum(ArrayList<Integer> list) {
       int total = 0;
       for (int i = 0; i < /* missing */; i++) {
           total += list.get(i);
       }
       return total;
   }

   Which expression correctly replaces /* missing */?

   • A

     list.size

   • B

     list.size()

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   • C

     list.length()

   • D

     list.length

   Why

   ArrayList uses size(), a method call. length is a property of arrays, and length() applies to Strings.

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2. Sample 2difficulty 2/5

   ArrayList<String> list = new ArrayList<>();
   list.add("hi");
   list.add("hello");
   list.add("hey");
   int total = 0;
   for (String s : list) total += s.length();
   System.out.println(total);

   What is printed?

   • A

     10

     check_circle
   • B

     8

   • C

     11

   • D

     3

   Why

   "hi"=2, "hello"=5, "hey"=3. Sum = 2+5+3 = 10.

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3. Sample 3difficulty 2/5

   ArrayList<Integer> list = new ArrayList<>();
   list.add(10);
   list.add(20);
   list.add(30);
   for (int i = 0; i < list.size(); i++) {
       list.set(i, list.get(i) + 1);
   }
   System.out.println(list);

   What is printed?

   • A

     [11, 22, 33]

   • B

     [1, 2, 3]

   • C

     [11, 21, 31]

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   • D

     [10, 20, 30]

   Why

   Each element is replaced by itself plus 1: 11, 21, 31.

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4. Sample 4difficulty 3/5

   import java.util.ArrayList;
   public static int run() {
       ArrayList<Integer> a = new ArrayList<>();
       for (int i = 1; i <= 4; i++) a.add(i * i);
       a.set(2, a.get(0) + a.get(3));
       int s = 0;
       for (int v : a) s += v;
       return s;
   }
   // Call: System.out.println(run());

   What is printed?

   • A

     33

   • B

     29

   • C

     38

     check_circle
   • D

     30

   Why

   a = [1,4,9,16]. a.set(2, 1+16=17) -> [1,4,17,16]. Sum = 38.

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5. Sample 5difficulty 3/5

   Sum all integers in <code>ArrayList<Integer> list</code>:

   • A

     for (int x : list) sum += x;

     check_circle
   • B

     Both work; first is enhanced-for, second uses size()

   • C

     for (int i = 0; i < list.length; i++) sum += list[i];

   • D

     Cannot iterate

   Why

   First works (with auto-unboxing); second has wrong syntax (use <code>list.size()</code> and <code>list.get(i)</code>).

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