Answer: 105 then 5 First call uses base=100 returning 105; after setting base to 0, the second call returns 5.

Answer: 36 Static methods are called on the class. square(6) returns 36.

Answer: 14 Although calling a static method through an instance is discouraged, it compiles; the method returns 14.

AP Computer Science A · Topic 5.7

Static Variables and Methods Practice

Part of Writing Classes.

Practice questions

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Sample questions

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Sample 1difficulty 2/5
```
public class Util {
    public static int base = 100;
    public static int boost(int x) {
        return base + x;
    }
}
// ...
System.out.println(Util.boost(5));
Util.base = 0;
System.out.println(Util.boost(5));
```
$What is printed?$
- A
  $105 then 5$
  check_circle
- B
  $5 then 5$
- C
  $Compile-time error$
- D
  $105 then 105$
Why
$First call uses base=100 returning 105; after setting base to 0, the second call returns 5.$
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Sample 2difficulty 2/5
```
public class MathUtil {
    public static int square(int n) { return n * n; }
}
// ...
System.out.println(MathUtil.square(6));
```
$What is printed?$
- A
  $36$
  check_circle
- B
  $12$
- C
  $6$
- D
  $Compile-time error$
Why
$Static methods are called on the class. square(6) returns 36.$
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Sample 3difficulty 2/5
```
public class Util {
    public static int doubleIt(int n) { return n * 2; }
}
// ...
Util u = new Util();
System.out.println(u.doubleIt(7));
```
$What is printed?$
- A
  $14$
  check_circle
- B
  $7$
- C
  $Compile-time error$
- D
  $0$
Why
$Although calling a static method through an instance is discouraged, it compiles; the method returns 14.$
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Sample 4difficulty 2/5

public class Circle {
    public static final double PI = 3.14159;
    private double r;
    public Circle(double r) { this.r = r; }
    public double area() { return PI * r * r; }
}
// ...
Circle c = new Circle(2);
System.out.println(c.area());

What is printed?

A
$12.56636$
check_circle
B
$6.28318$
C
$3.14159$
D
$Compile-time error$

Why

area is PI * 2 * 2 = 3.14159 * 4 = 12.56636.

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Sample 5difficulty 3/5

public class Money {
    private int cents;
    private Money(int c) { cents = c; }
    public static Money fromDollars(int d) {
        return new Money(d * 100);
    }
    public int getCents() { return cents; }
}
// ...
Money m = Money.fromDollars(3);
System.out.println(m.getCents());

What is printed?

A
$3$
B
$100$
C
$Compile-time error$
D
$300$
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Why

The static factory invokes the private constructor with 300, which is stored in cents.

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