Java important question - 10

Can we use String with switch case ?

          One of the java7 features was improvement of switch case to allow strings. So if you are using java 7 or higher version, you can use String in switch case statement.

private static void printColorUsingSwitch                                                (String color) {

switch(color) {

case "blue":

     System.out.println("Blue");

     break;

case "red":

     System.out.println("Red");

     break;

default :

     System.out.println("Invalid color       

                                       code");

}

Q) Difference between String, StringBuilder and StringBuffer in java

String :

          String is immutable object. The object created as a string is stored in the Constant string pool. Every immutable object in Java is thread safe, that implies string is also thread safe. String cannot be used by two threads simultaneously. 

          String once assigned cannot be changed.

String demo = "hello";

     // The above object is stored in constant string pool and it's value cannot be modified.

demo ="Bye";

     // new "Bye" string is created in constant pool and referenced by the demo variables

     // "hello" string still exists in string constant pool and it's value is not overridden but we lost referenced to the "hello" string

StringBuffer

          StringBuffer is mutable means one can change the value of the object. The object created through StringBuffer is stored in the heap. StringBuffer has the same methods as the StringBuilder, but each method in StringBuffer is synchronized that is StringBuffer is thread safe. Due to this it does not allow two threads to simultaneously access the same method. Each method can be accessed by one thread at a time. But being thread safe has disadvantage too as the performance of the StringBuffer hits due to thread safe property. Thus StringBuilder is faster than the StringBuffer when calling the same method of each class. 

     StringBuffer value can be changed, it means it can be assigned to the new value.

     StringBuffer can be converted to the string by using toString() method.

StringBuffer demo1 = new StringBuffer                                            ("Hello");

// The above object stored in heap and it's value can be changed.

demo1 = new StringBuffer ("Bye");

// The above statement is right as it modifies the value which is allowed in the StringBuffer

StringBuilder:

          StringBuilder is same as the StringBuffer, it stores the object in heap and it can also be modified. The main difference between the StringBuffer and StringBuilder is that StringBuilder is not synchronized. StringBuilder is fast as it is not thread safe.

StringBuilder demo2 = new StringBuilder                                          ("Hello");

// The above object too is stored in the heap and it's value can be modified.

demo2 = new StringBuilder ("Bye");

// The above statement is right as it's modifies the value which is allowed in the StringBuilder.

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