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Discussion :: Java.lang Class

  1. Which two statements are true about wrapper or String classes?

    1. If x and y refer to instances of different wrapper classes, then the fragment x.equals(y) will cause a compiler failure.
    2. If x and y refer to instances of different wrapper classes, then x == y can sometimes be true.
    3. If x and y are String references and if x.equals(y) is true, then x == y is true.
    4. If x, y, and z refer to instances of wrapper classes and x.equals(y) is true, and y.equals(z) is true, then z.equals(x) will always be true.
    5. If x and y are String references and x == y is true, then y.equals(x) will be true.

  2. A.
    1 and 2
    B.
    2 and 3
    C.
    3 and 4
    D.
    4 and 5

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    Answer : Option D

    Explanation :

    Statement (4) describes an example of the equals() method behaving transitively. By the way, x, y,and z will all be the same type of wrapper. Statement (5) is true because x and y are referring to the same String object.

    Statement (1) is incorrect—the fragment will compile. Statement (2) is incorrect because x == y means that the two reference variables are referring to the same object. Statement (3) will only be true if x and y refer to the same String. It is possible for x and y to refer to two different String objects with the same value.


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