Top Most String class Interview questions

·         It is final.

·         String objects are immutable.

Not methods of this class –append, delete, insert. Hence a code fragment like this causes compiler error ,

String s = “A”;

s.trim();s.append();//causes compiler error since append is not String method

·         “valueOf” is static method of String class.

·         String has many constructors ,some of the important ones take input parameters

Ø  string

Ø  stringBuffer

Ø  byte array

Ø  char array

Ø  Doesn’t take in any argument.

→ String constructor doesn’t take in parameter such as char, byte, int, short,

int array  ,any array other than char array and byte array etc .

·         String class has a method called length() where as array has attribute called ‘length’

hence, String s = “abcd”;

                        int a = s.length;//causes error

similarlay

                        int [] a = {1,2,3,4,5};

                        int b = a.length();//causes error

·         String s1  = new String(“abcd”);

String s2 = s1.toString();

here toString method returns the reference to the existing object hence

“s1==s2” will be true.

Note: Even substring(),trim(),concat(),return the same string if they don’t modify the given string.

·         String s1 = “santosh”;

String s2 = “santosh”;

then “s1==s2” is true ,since while creating a string object the compiler looks for the same String in the pool and if it finds one then it returns the reference to the existing string.

Note: given ,

      String s ,s1 ,s2,s3;

      s=s1=s2=s3=null;

      {….compelx code….}

      s=s1+s2;

      s3 = s1+s2;

      then “s == s3“ will return false.