Java Interview Questions – Part 2

Java Interview Questions – Part 2

String is Immutable. (String Details with Example Here)

1. What is meant by Immutable?
   In Java, Strings are treated as Objects. Immutable means once the object has been created it cannot be changed.
2. What are the advantages of String being Immutable?
   • It helps in Multi-threading, We can be sure that no one will change the string
   • Reduction in Memory usage
3. Two ways of Creating Strings:
   • String s1 = “StringValue”;
   • String S2 = new String(“StringValue2”);
4. What is the difference between creating Strings?
   Consider an example,
   • We are creating 2 strings with S1 and S2,
   • String S1 = “Java”
   • String S2 = “Java”
   • This will create a single reference in string pool and S1 and S2 will point to that Reference
   • String S1 = new String(“Java”)
   • String S2 = new String(“Java”)
   • This will create two separate objects in string pool
   • String s1 = “Java”, String S2 = “Java”
   • 
   • String S1 = new String(“Java”), String S2 = new String(“Java”)
     
5. Difference Between StringBuilder and StringBuffer:
   

   StringBuilder	StringBuffer
   StringBuilder is mutable	StringBuffer is mutable
   StringBuilder is unsynchronized	StringBuffer is Synchronized
   StringBuilder is faster	StringBuffer is slower when compared to StringBuilder

   NOTE: StringBuffer and StringBuilder does not Override equals() and hashcode()

6. When to use String, StringBuffer and StringBuilder?
   If our string is not going change, We use String.
   If our string can change and accessed only from single thread, We can use StringBuilder.
   If our string can change and can be accessed from multiple threads, We can use StringBuffer.
7. Difference between == and Equals()
   • == : Will check if the address of the values are same and NOT the values itself
   • Equals(): Will check if both the values are equals
   • Example:
     • String S1 = “Java”, String S2 = “Java”
       S1==S2 will be True
     • String S1 = new String(“Java”), String S2 = new String(“Java”)
       Here S1 == S2 will be false, But S1.equals(S2) will be true
8. Important Points:
   • Strings are Thread Safe
   • String Pool is stored in Heap Memory

(For Detailed Example of Strings, StringBuffer and StringBuilder, Click Here)

Arrays:

1. What is an Array?
   Arrays are objects in Java that store multiple Variables of Same Type
2. Declaring an Array?
   int[] array1;
3. Can we declare an Array without its Size?
   Consider, We are constructing and array without mentioning the Size,
   • int[] Array1 = new int[];
     This line will not get Compiled, As the size of array is required.
4. How does array store the values in memory?
   
5. How to declare array with values in single line?
   • int array1 = {4,5,6};
6. Arrays Holding Objects?
   • A[][] a = {{new A(“value1”), new A(“value2”)}, {new A(“value3”), new A(“value4”)}}