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Asked multiple times in Capgemini.

Q61. Why Char array is preferred over String for storing password?

Ans. String is immutable in java and stored in String pool. Once it's created it stays in the pool until unless garbage collected, so even though we are done with password it's available in memory for longer duration and there is no way to avoid it. It's a security risk because anyone having access to memory dump can find the password as clear text.

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Q62. Why String is popular HashMap key in Java?

Ans. Since String is immutable, its hashcode is cached at the time of creation and it doesnt need to be calculated again. This makes it a great candidate for key in a Map and its processing is fast than other HashMap key objects. This is why String is mostly used Object as HashMap keys.

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Q63. public class a {
   public static void main(String args[]){
      final String s1=""job"";
      final String s2=""seeker"";
      String s3=s1.concat(s2);
      String s4=""jobseeker"";
      System.out.println(s3==s4); // Output 1
      System.out.println(s3.hashCode()==s4.hashCode()); Output 2
   }
}

What will be the Output 1 and Output 2 ?

Ans. S3 and S4 are pointing to different memory location and hence Output 1 will be false.

Hash code is generated to be used as hash key in some of the collections in Java and is calculated using string characters and its length. As they both are same string literals, and hence their hashcode is same.Output 2 will be true.

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Q64. What is the use of HashCode in objects ?

Ans. Hashcode is used for bucketing in Hash implementations like HashMap, HashTable, HashSet etc.

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Q65. What does String intern() method do?

Ans. intern() method keeps the string in an internal cache that is usually not garbage collected.

Moreover provide reference for scp object for corresponding string object present in heap memory.

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Q66. How substring() method of String class create memory leaks?

Ans. substring method would build a new String object keeping a reference to the whole char array, to avoid copying it. Hence you can inadvertently keep a reference to a very big character array with just a one character string.

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Very frequently asked in HCL Tech ( Based of 4 inputs )

Q67. Write a program to reverse a string iteratively and recursively ?

Ans. Using String method -

new StringBuffer(str).reverse().toString();

Iterative -

public static String getReverseString(String str){
StringBuffer strBuffer = new StringBuffer(str.length);
for(int counter=str.length -1 ; counter>=0;counter--){
strBuffer.append(str.charAt(counter));
}
return strBuffer;
}

Recursive -

public static String getReverseString(String str){
if(str.length <= 1){
return str;
}
return (getReverseString(str.subString(1)) + str.charAt(0);
}

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Q68. What will be the output of the following code ?

String s1 = "Buggy Bread";
String s2 = "Buggy Bread";
if(s1 == s2)
System.out.println("equal 1");
String n1 = new String("Buggy Bread");
String n2 = new String("Buggy Bread");
if(n1 == n2)
System.out.println("equal 2");

Ans. equal 1

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Q69. What will be the output of following Code ?

class BuggyBread {
   public static void main(String[] args) {
      String s2 = "I am unique!";
      String s5 = "I am unique!";

      System.out.println(s2 == s5);
   }
}

Ans. true, due to String Pool, both will point to a same String object.

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Q70. what will be the output of this code ?

public static void main(String[] args){
   StringBuffer s1=new StringBuffer("Buggy");
   test(s1);
   System.out.println(s1);
}

private static void test(StringBuffer s){
   s.append("Bread");
}

Ans. BuggyBread

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Q71. what will be the output of this code ?

public static void main(String[] args)    {
   String s1=new String("Buggy");
   test(s1);
   System.out.println(s1);
}

private static void test(StringBuffer s){
   s.append("Bread");
}

Ans. Buggy

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Q72. what will be the output of this code ?

public static void main(String[] args)    {
   StringBuffer s1=new StringBuffer("Buggy");
   test(s1);
   System.out.println(s1);
}

private static void test(StringBuffer s){
   s=new StringBuffer("Bread");
}

Ans. Buggy

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Q73. Which methods of the Pattern class have equivalent methods in the String class?

Ans. split() and macthes()

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Q74. public class BuggyBread1{

public static void main (String args[]) {
Set<String> mySet = new TreeSet<String>();
mySet.add(""1"");
mySet.add(""2"");
mySet.add(""111"");
for(String d: mySet){
System.out.println(d);
}
}
}

Ans. 1
111
2

TreeSet maintains the elements in the ascending order which is identified by the compareTo method. compareTo method in String has been defined such that it results in the natural alphabetic Order. Here the elements in the TreeSet are of String and not of Integer. In String Natural Order, 111 comes before 2 as ascii of 1st character first determines the order.

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Q75. Give an Example for Builder Pattern ?

Ans. String str = new StringBuilder().append("Buggy").append("Bread").toString();

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Not frequently asked as it was introduced with Java 8.

Q76. What is StringJoiner ?

Ans. StringJoiner is a util method to construct a string with desired delimiter. This has been introduced with wef from Java 8.

Sample Code

StringJoiner strJoiner = new StringJoiner(".");

strJoiner.add("Buggy").add("Bread");

System.out.println(strJoiner); // prints Buggy.Bread

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Q77. Have you ever used StringTokenizer ?

Ans. No, Alternatively I have used String.split("\\s") for achieving the same function.

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Q78. Name few String related classes and interfaces ?

Ans. http://www.buggybread.com/2015/01/java-string-classes-and-interfaces.html

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Q79. How many elements will be there in TreeSet after the last line and Why ?

TreeSet set = new TreeSet();
set .add(new String("abc"));
set .add(new String("abc"));

Ans. One.

As we haven't specified the type of TreeSet, it being evaluated with the first element insertion. Once it's identified that it's of type String and as no comparator has been defined, the comparison is done using the String compareTo method. String compareTo method compares the elements by the content / value.

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Q80. Strings in switch were introduced in Which Java version ? a. Java 5 b. Java 6 c. Java 7 d. Java

Ans. Java 7

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Rarely asked as it was introduced with Java 8.

Q81. Which of the following has been introduced with Java 8 ? a. StringBuffer b. StringBuilder c. StringFilter d. StringJoiner

Ans. StringJoiner

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Q82. Write a method to convert all elements of a set to lower case.

Ans. http://javasearch.buggybread.com/CodeSnippets/searchCodeSamples.php?keyword=Method+to+convert+all+elements+of+a+collection&category=code

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Q83. Write java code to Get all words from a String and display them

Ans. http://javasearch.buggybread.com/CodeSnippets/searchCodeSamples.php?keyword=+Get+all+words+from+a+String&category=code

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Q84. What will be the output of following code ?

String str1 = "String1";
String str2 = "String1";
System.out.print(str1 == str2);
System.out.print(str1.equals(str2));
str1 = str2;
System.out.print(str1 == str2);

a. falsetruetrue

b. falsefalsetrue

c. truetruetrue

d. falsefalsefalse

Ans.c. truetruetrue

Q85. Which of the following class creates immutable objects ? Reference

a. String

b. StringBuffer

c. StringBuilder

d. None of these create immutable objects.

Ans.a. String

Q86. Which of the following class is synchronized ? Reference

a. String

b. StringBuffer

c. StringBuilder

d. None of these

Ans.b. StringBuffer

Q87. Which memory segment holds String Pool ?

a. Stack

b. Heap

c. Code Segment

d. Class Segment

Ans.b. Heap

Q88. Which of the following class cannot be extended or inherited ?

StringBuffer , StringBuilder

a. StringBuffer

b. StringBuilder

c. Both cannot be extended

d. Both can be extended

Ans.c. Both cannot be extended

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