Oct 8, 2026 ·Name: ____________________ Period: ______

Part 1: Easy

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1. What is printed?

int[] a = {3, 1, 4, 1, 5};
int sum = 0;
for (int i = 0; i < a.length; i++)
    sum += a[i];
System.out.println(sum);

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Output: ______________

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2. What are the contents of a after this code runs?

int[] a = {2, 4, 6, 8, 10};
a[1] = a[3];
a[4] = a[0] + a[2];

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a = ______________________

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3. What are the contents of a, and what is the value of a[2] + a[4]?

int[] a = new int[5];
for (int i = 0; i < a.length; i++)
    a[i] = i * i;

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a = ______________________ a[2] + a[4] = ________

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4. What are the final values of max and updates?

int[] a = {5, 2, 8, 1, 9};
int max = a[0];
int updates = 0;
for (int i = 1; i < a.length; i++) {
    if (a[i] > max) {
        max = a[i];
        updates++;
    }
}

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max = ________ updates = ________

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5. What is printed? (Watch the loop update.)

String[] w = {"cat", "dog", "bird", "fish"};
for (int i = w.length - 1; i >= 0; i -= 2)
    System.out.print(w[i] + " ");

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Output: ______________

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Part 2: Medium

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6. What are the contents of a after this code runs?

int[] a = {1, 2, 3, 4, 5};
int first = a[0];
for (int i = 0; i < a.length - 1; i++)
    a[i] = a[i + 1];
a[a.length - 1] = first;

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a = ______________________

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7. What are the contents of a after this code runs?

int[] a = {3, -1, 4, -2, 5};
for (int i = 1; i < a.length; i++)
    a[i] += a[i - 1];

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a = ______________________

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8. What are the final values of count and total?

int[] a = {4, 7, 2, 9, 6, 3};
int count = 0, total = 0;
for (int x : a) {
    if (x % 2 == 0) {
        count++;
        total += x;
    } else {
        total -= x;
    }
}

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count = ________ total = ________

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9. What are the contents of a after this code runs?

int[] a = {1, 2, 3, 4, 5};
for (int i = 0; i < a.length - 1; i += 2) {
    int t = a[i];
    a[i] = a[i + 1];
    a[i + 1] = t;
}

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a = ______________________

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10. Draw a box-and-arrow diagram if it helps. What is printed?

int[] a = {1, 2, 3};
int[] b = a;
int[] c = {1, 2, 3};
b[0] = 9;
c[1] = b[2] + 1;
System.out.println(Arrays.toString(a));
System.out.println(Arrays.toString(c));
System.out.println(a == b);
System.out.println(a == c);

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Line 1: ______________ Line 2: ______________ Line 3: ________ Line 4: ________

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Part 3: Challenging

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11. (Nested loops) What are the contents of r after this code runs?

int[] a = {5, 3, 5, 1, 4};
int[] r = new int[a.length];
for (int i = 0; i < a.length; i++)
    for (int j = 0; j < a.length; j++)
        if (a[j] < a[i])
            r[i]++;

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r = ______________________

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12. (A method that modifies an array) Consider this method:

public static void mystery(int[] arr, int n) {
    for (int i = 0; i < arr.length; i++)
        arr[i] += n;
    arr = new int[]{0, 0, 0};
    n = 100;
    arr[0] = n;
}

What are the contents of data and the value of k after this code runs?

int[] data = {1, 2, 3};
int k = 5;
mystery(data, k);

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data = ______________________ k = ________

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13. (A method that modifies its parameter and returns a new array) Consider this method:

public static int[] process(int[] a) {
    int[] result = new int[a.length];
    for (int i = 0; i < a.length; i++) {
        result[i] = a[i] * 2;
        if (i > 0)
            a[i - 1] = result[i];
    }
    return result;
}

What are the contents of a and b after this code runs?

int[] a = {1, 2, 3, 4};
int[] b = process(a);

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a = ______________________ b = ______________________

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14. (Array of objects) Consider this class:

public class Counter {
    private String name;
    private int count;
    public Counter(String name) { this.name = name; this.count = 0; }
    public void increment() { count++; }
    public String toString() { return name + ":" + count; }
}

What is printed by the last line of this code?

Counter[] cs = new Counter[3];
for (int i = 0; i < cs.length; i++)
    cs[i] = new Counter("c" + i);
Counter x = cs[1];
cs[2] = x;
x.increment();
cs[0].increment();
cs[2].increment();
cs[1] = new Counter("new");
cs[1].increment();
System.out.println(cs[0] + " " + cs[1] + " " + cs[2] + " " + x);

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Output: ______________________________________

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15. (Array of arrays) What are the contents of g after this code runs? Write it as three rows.

int[][] g = {{1, 2, 3}, {4, 5, 6}, {7, 8, 9}};
for (int r = 0; r < g.length; r++) {
    for (int c = r + 1; c < g[r].length; c++) {
        int t = g[r][c];
        g[r][c] = g[c][r];
        g[c][r] = t;
    }
}
int[] row = g[0];
g[0] = g[2];
g[2] = row;
for (int r = 0; r < g.length; r++)
    g[r][r] = 0;

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Row 0: ______________ Row 1: ______________ Row 2: ______________

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16. (Array of objects, shared references) Consider this class and these methods:

public class Player {
    private String name;
    private int pts;
    public Player(String name, int pts) { this.name = name; this.pts = pts; }
    public void add(int n) { pts += n; }
    public String toString() { return name + "=" + pts; }
}

public static void swap(Player[] ps, int i, int j) {
    Player t = ps[i];
    ps[i] = ps[j];
    ps[j] = t;
}

public static void bonus(Player[] ps) {
    for (Player p : ps)
        p.add(5);
    ps = new Player[]{new Player("X", 0)};
    ps[0].add(1);
}

What is printed by the last line of this code?

Player[] ps = {new Player("A", 10), new Player("B", 20), new Player("C", 30)};
Player top = ps[2];
swap(ps, 0, 2);
bonus(ps);
top.add(100);
System.out.println(ps[0] + " " + ps[1] + " " + ps[2] + " " + top);

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Output: ______________________________________

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17. (Calling a method that modifies the array twice) Consider this method:

public static void shiftRight(int[] a) {
    for (int i = a.length - 1; i > 0; i--)
        a[i] = a[i - 1];
}

What are the contents of a after this code runs?

int[] a = {1, 2, 3, 4, 5};
shiftRight(a);
shiftRight(a);
a[0] = a[a.length - 1] + a[1];

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a = ______________________

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18. (Jagged array) What is printed?

int[][] t = new int[4][];
int total = 0;
for (int i = 0; i < t.length; i++) {
    t[i] = new int[i + 1];
    t[i][0] = 1;
    t[i][i] = 1;
    for (int j = 1; j < i; j++)
        t[i][j] = t[i - 1][j - 1] + t[i - 1][j];
    for (int v : t[i])
        total += v;
}
System.out.println(Arrays.toString(t[3]) + " " + total);

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Output: ______________________________________

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19. (Shifting inside a loop) What are the final values of n and the contents of a?

int[] a = {2, 2, 3, 3, 3, 5, 2};
int n = 1;
for (int i = 1; i < a.length; i++) {
    if (a[i] != a[n - 1]) {
        a[n] = a[i];
        n++;
    }
}

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n = ________ a = ______________________

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20. (Array of arrays with aliased rows) What is printed?

int[][] g = new int[2][2];
int[] r = {1, 2};
g[0] = r;
g[1] = r;
g[0][0] = 7;
r = new int[]{9, 9};
g[1][1] = g[0][0] + 1;
System.out.println(Arrays.deepToString(g));
System.out.println(Arrays.toString(r));

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Line 1: ______________________________ Line 2: ______________

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Answer key (teacher copy)

Every answer below was checked by compiling and running the code. Delete this section before copying the worksheet for students.

# Answer What it tests
1 14 Accumulator over an array
2 [2, 8, 6, 8, 8] Index assignment; a[4] = 2 + 6
3 [0, 1, 4, 9, 16]; 4 + 16 = 20 Filling with a loop
4 max = 9, updates = 2 Running max; only 8 and 9 beat the max
5 fish dog Counting down by 2
6 [2, 3, 4, 5, 1] Left rotation
7 [3, 2, 6, 4, 9] Running sums use already-updated values
8 count = 3, total = -7 Enhanced for; evens 4+2+6 = 12 added, odds 7+9+3 = 19 subtracted
9 [2, 1, 4, 3, 5] Pair swaps; the last element has no partner
10 [9, 2, 3]; [1, 4, 3]; true; false Aliasing: b is a, c is a separate array
11 [3, 1, 3, 0, 2] Counting smaller elements; equal values are not counted
12 data = [6, 7, 8]; k = 5 Elements change through the reference; reassigning arr and n has no effect outside
13 a = [4, 6, 8, 4]; b = [2, 4, 6, 8] Method mutates its parameter; result is separate
14 c0:1 new:1 c1:2 c1:2 Two references to one object; cs[1] is reassigned, x still points to the old c1
15 [0, 6, 9], [2, 0, 8], [1, 4, 0] Transpose, row swap by reference, then zero the diagonal
16 C=135 B=25 A=15 C=135 Array of objects; swap moves references; enhanced for mutates the objects
17 [4, 1, 1, 2, 3] Repeated calls to a mutating method; a[0] uses the shifted values
18 [1, 3, 3, 1] 15 Jagged array (Pascal’s triangle); row sums 1 + 2 + 4 + 8
19 n = 4; [2, 3, 5, 2, 3, 5, 2] Compact in place; the tail past n is left over from the original
20 [[7, 8], [7, 8]]; [9, 9] Both rows are one array; reassigning r afterwards does not affect g

Notes on the trickiest ones

  • 12: arr starts as an alias of data, so the += n loop changes the caller’s array. Then arr = new int[]{0, 0, 0} points the local variable elsewhere, so arr[0] = n touches only the new array.
  • 13: At i = 1, a[0] becomes 4, and so on. The last element of a is never overwritten, so it stays 4. Students often forget that a itself changed.
  • 14: After cs[2] = x, slots 1 and 2 and x all name the same object. It is incremented twice (c1:2). cs[1] = new Counter("new") only repoints slot 1.

  • 15: After the transpose, g is {{1,4,7},{2,5,8},{3,6,9}}. Swapping g[0] and g[2] swaps whole row references, giving {{3,6,9},{2,5,8},{1,4,7}}. Zeroing the diagonal gives the final answer.

  • 16: After swap, slot 0 holds C and slot 2 holds A. bonus adds 5 to every object, so C is 35, B is 25, A is 15. The new array inside bonus is thrown away. top still refers to C, so top.add(100) makes C 135, and it shows in slot 0 as well.
  • 17: One call gives {1,1,2,3,4}, two give {1,1,1,2,3}. Then a[0] = 3 + 1 = 4.
  • 18: The rows are {1}, {1,1}, {1,2,1}, {1,3,3,1}, so total is 15. Students who think every row has 4 columns get an out-of-bounds error.
  • 19: Only positions 0 to 3 are meaningful after the loop (n = 4). Positions 4 to 6 still hold the original 3, 5, 2, which is why the array ends in {…, 3, 5, 2}.
  • 20: After g[0] = r; g[1] = r; both rows are the same array. Writing 7 and then 8 changes that one array, giving {7, 8}. r = new int[]{9, 9} repoints only the variable r.