What is wrong with this method?

Answer: Strings should be compared with .equals, not == == compares object references for Strings, not contents. Use s.equals("hello") to compare characters; == may succeed for literals due to interning but fails generally.

To check if <codeString s</code equals <code"yes"</code, use

Answer: s.equals("yes") Use <code.equals</code for string content comparison; <code==</code only checks references.

For <codeString a = new String("hi"); String b = new String("hi");</code — what is <codea == b</code and <codea.equals(b)</code?

Answer: == false; equals true <code==</code compares references (different objects → false); <code.equals</code compares content (same content → true).

AP Computer Science A · Topic 3.7

Comparing Objects Practice

Q: To check if <codeString s</code equals <code"yes"</code, use

Answer: s.equals("yes") Use <code.equals</code for string content comparison; <code==</code only checks references.

Q: For <codeString a = new String("hi"); String b = new String("hi");</code — what is <codea == b</code and <codea.equals(b)</code?

Answer: == false; equals true <code==</code compares references (different objects → false); <code.equals</code compares content (same content → true).

Part of Boolean Expressions and if Statements.

Practice questions

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Sample questions

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Sample 1difficulty 2/5
```
public static boolean isHello(String s) {
    if (s == "hello") {
        return true;
    }
    return false;
}
```
$What is wrong with this method?$
- A
  $The if-statement is missing braces$
- B
  $The method should return s instead of true$
- C
  $Nothing is wrong; it works correctly for all inputs$
- D
  $Strings should be compared with .equals, not ==$
  check_circle
Why
$== compares object references for Strings, not contents. Use s.equals("hello") to compare characters; == may succeed for literals due to interning but fails generally.$
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Sample 2difficulty 4/5
$To check if <code> String s </code> equals <code> "yes" </code>, use$
- A
  $s.equals("yes")$
  check_circle
- B
  $s.compareTo("yes")$
- C
  $s == "yes"$
- D
  $s == 'yes'$
Why
$Use <code> .equals </code> for string content comparison; <code> == </code> only checks references.$
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Sample 3difficulty 4/5
$For <code> String a = new String("hi"); String b = new String("hi"); </code> — what is <code> a == b </code> and <code> a.equals(b) </code> ?$
- A
  $== true; equals false$
- B
  $Both false$
- C
  $Both true$
- D
  $== false; equals true$
  check_circle
Why
$<code> == </code> compares references (different objects \to false); <code> .equals </code> compares content (same content \to true).$
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Sample 4difficulty 4/5
$Why is <code> if (0.1 + 0.2 == 0.3) </code> unreliable?$
- A
  $Always works$
- B
  $Round-off error in floating-point representation$
  check_circle
- C
  $0.1 isn't a valid number$
- D
  $Doubles can't be compared$
Why
$Binary FP cannot represent 0.1 exactly; 0.1+0.2 = 0.30000000000000004.$
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Sample 5difficulty 4/5
$<code> s.equals(null) </code> (where s is non-null) returns$
- A
  $Throws NullPointerException$
- B
  $true$
- C
  $false$
  check_circle
- D
  $Compile error$
Why
$Equals returns false for null comparison; doesn't throw.$
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