Java-Interview-Questions-&-Answers by BestOnlineTrainers (1)

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Java Interview Q A

• By www.bestonlinetrainers.com

2
Q21 How are strings compared Using or
equals ()?

• Answer
• tests if references are equal and equals ()
  tests if values are equal. To check if two
  strings are the same object, equals() is always
  used.

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3
Q22 Char is preferred over String for security
sensitive information. Why?

• Answer
• Strings are immutable, that is once they are
  created, and they stay unchanged until Garbage
  Collector kicks in. Its elements can be
  explicitly changed with an array. Hence, security
  sensitive information like password will not be
  present anywhere in the system.

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4
Q23WCan string be used to switch statement?

• Answer
• String can be used to switch statement to
  version 7. From JDK 7, string can be used as
  switch condition. Before version 6, string cannot
  be used as switch condition .
• view source
• print?
• 01.// java 7 only!
• 02.switch (str.toLowerCase())
• 03.case "a"
• 04.value 1
• 05.break
• 06.case "b"
• 07.value 2
• 08.break
• 09.

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Q24Can string be converted to int?

• Answer
• If the HashCode() is not overridded , the
  object will not be recovered from the HashMap if
  used as key.
• Yes .It can be .But its frequently used and
  ignored at times.
• view source
• print?
• 1.int n Integer.parseInt("10")

6
Q25 How can a string be split with white space
characters?

• Answer
• String can be slit using regular expression.
  White space characters are represented as \s.
• view source
• print?
• 1 .String strArray aString.split("\\s")

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Q26 What does substring() method do ?

• Answer
• The existing String is represented by the
  substring() method which gives a window to an
  array of chars as in JDK 6.A new one is not
  created. An empty string needs to be added to
  create a new one.
• print
• ?
• 1.str.substring(m,n) ""
• This creates a new char array representing a new
  string. This method can help to code faster
  because the Garbage Collector collects the unused
  large string and the keeps the substring.

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Q27 What is String vs StringBuilder vs
StringBuffer ?

• Answer
• In String vs StringBuilder, StringBuilder
  is mutable, that is it means it can be modified
  after its creation. In StringBuilder vs
  StringBuffer, StringBuffer is synchronized, that
  is it means it is thread-safe but would be slower
  than StringBuilder.

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Q28 How is a string repeated ?

• Answer
• In Python, to repeat a string just multiple
  a number. In Java, the repeat() method of
  StringUtils from Apache Commons Lang package can
  be used.

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Q29 In Java, what is the default value of byte
datatype?

• Answer
• 0 is the default value of byte datatype.

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Q30 In a string how to count of occurrences of
a character?

• Answer
• StringUtils from apache commons lang can be
  used.
• view source
• print?
• 1.int n StringUtils.countMatches("11112222",
  "1")
• 2.System.out.println(n)

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