Answer: 10 The Integer x is auto-unboxed to int 7 when used in arithmetic, so y = 7 + 3 = 10.

Answer: 43 Integer.parseInt converts the string "42" to the int 42; adding 1 gives 43.

Answer: 9.0 d is auto-unboxed to double 4.5; multiplying by 2 yields 9.0.

AP Computer Science A · Topic 2.8

Wrapper Classes: Integer and Double Practice

Part of Using Objects.

Practice questions

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Sample questions

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Sample 1difficulty 2/5
```
Integer x = 7;
int y = x + 3;
System.out.println(y);
```
$What is printed?$
- A
  $10$
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- B
  $7$
- C
  $37$
- D
  $73$
Why
$The Integer x is auto-unboxed to int 7 when used in arithmetic, so y = 7 + 3 = 10.$
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Sample 2difficulty 3/5
```
String s = "42";
int n = Integer.parseInt(s);
System.out.println(n + 1);
```
$What is printed?$
- A
  $421$
- B
  $42$
- C
  $Error$
- D
  $43$
  check_circle
Why
$Integer.parseInt converts the string "42" to the int 42; adding 1 gives 43.$
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Sample 3difficulty 3/5
```
Double d = 4.5;
double r = d * 2;
System.out.println(r);
```
$What is printed?$
- A
  $9.0$
  check_circle
- B
  $4.5$
- C
  $9$
- D
  $8.5$
Why
$d is auto-unboxed to double 4.5; multiplying by 2 yields 9.0.$
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Sample 4difficulty 3/5
$Which is the wrapper class for the <code> int </code> primitive?$
- A
  $Integer$
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- B
  $Int$
- C
  $IntegerType$
- D
  $INT$
Why
$<code> Integer </code> wraps int; <code> Double </code> wraps double; <code> Boolean </code> wraps boolean.$
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Sample 5difficulty 3/5
```
String s = "3.14";
double d = Double.parseDouble(s);
System.out.println(d * 2);
```
$What is printed?$
- A
  $6.28$
  check_circle
- B
  $Error$
- C
  $6$
- D
  $3.14$
Why
$Double.parseDouble converts the string "3.14" to the double value 3.14; multiplied by 2 the result is 6.28.$
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