String (Data link)
What is String in Java? String is a data type?
String is a Class in java and defined in java.lang package. It’s not a primitive data type like int and long. String class represents character Strings. String is used in almost all the Java applications and there are some interesting facts we should know about String. String is immutable and final in Java and JVM uses String Pool to store all the String objects.
Some other interesting things about String is the way we can instantiate a String object using double quotes and overloading of “+” operator for concatenation.
What are different ways to create String Object?
We can create String object using new operator like any normal java class or we can use double quotes to create a String object. There are several constructors available in String class to get String from char array, byte array, StringBuffer and StringBuilder.
String str = new String("abc");
String str1 = "abc";
When we create a String using double quotes, JVM looks in the String pool to find if any other String is stored with the same value. If found, it just returns the reference to that String object else it creates a new String object with given value and stores it in the String pool.
When we use the new operator, JVM creates the String object but don’t store it into the String Pool. We can use intern() method to store the String object into String pool or return the reference if there is already a String with equal value present in the pool.
Write a method to check if input String is Palindrome?
A String is said to be Palindrome if it’s value is same when reversed. For example “aba” is a Palindrome String.
String class doesn’t provide any method to reverse the String but StringBuffer and StringBuilder class has reverse method that we can use to check if String is palindrome or not.
private static boolean isPalindrome(String str) {
if (str == null)
return false;
StringBuilder strBuilder = new StringBuilder(str);
strBuilder.reverse();
return strBuilder.toString().equals(str);
}
Sometimes interviewer asks not to use any other class to check this, in that case, we can compare characters in the String from both ends to find out if it’s palindrome or not.
private static boolean isPalindromeString(String str) {
if (str == null)
return false;
int length = str.length();
System.out.println(length / 2);
for (int i = 0; i < length / 2; i++) {
if (str.charAt(i) != str.charAt(length - i - 1))
return false;
}
return true;
}
Write a method that will remove given character from the String?
We can use replaceAll method to replace all the occurance of a String with another String. The important point to note is that it accepts String as argument, so we will use Character class to create String and use it to replace all the characters with empty String.
private static String removeChar(String str, char c) {
if (str == null)
return null;
return str.replaceAll(Character.toString(c), "");
}
How can we make String upper case or lower case?
We can use String class toUpperCase and toLowerCase methods to get the String in all upper case or lower case. These methods have a variant that accepts Locale argument and use that locale rules to convert String to upper or lower case.
How to compare two Strings in java program?
Java String implements Comparable interface and it has two variants of compareTo() methods.
compareTo(String anotherString) method compares the String object with the String argument passed lexicographically. If String object precedes the argument passed, it returns negative integer and if String object follows the argument String passed, it returns a positive integer. It returns zero when both the String have the same value, in this case equals(String str) method will also return true.
compareToIgnoreCase(String str): This method is similar to the first one, except that it ignores the case. It uses String CASE_INSENSITIVE_ORDER Comparator for case insensitive comparison. If the value is zero then equalsIgnoreCase(String str) will also return true.
Check this post for String compareTo example.
How to convert String to char and vice versa?
This is a tricky question because String is a sequence of characters, so we can’t convert it to a single character. We can use use charAt method to get the character at given index or we can use toCharArray() method to convert String to character array.
Check this post for sample program on converting String to character array to String.
How to convert String to byte array and vice versa?
We can use String getBytes() method to convert String to byte array and we can use String constructor new String(byte[] arr) to convert byte array to String.
Check this post for String to byte array example.
Can we use String in switch case?
This is a tricky question used to check your knowledge of current Java developments. Java 7 extended the capability of switch case to use Strings also, earlier Java versions don’t support this.
If you are implementing conditional flow for Strings, you can use if-else conditions and you can use switch case if you are using Java 7 or higher versions.
Check this post for Java Switch Case String example.
Write a program to print all permutations of String?
This is a tricky question and we need to use recursion to find all the permutations of a String, for example “AAB” permutations will be “AAB”, “ABA” and “BAA”.
We also need to use Set to make sure there are no duplicate values.
Check this post for complete program to find all permutations of String.
- WAP to Reverse a String
- WAP to check palindrome
- WAP to find max and min occurring char in String
- WAP to count the number of words in String
- WAP to print all permutations of a String
- WAP to print the duplicate character from the given String
- WAP to remove the characters from 1st String which are present in 2nd String
- WAP to find non-repetitive characters in string
- WAP to check if strings are anagram of each other
- WAP to split comma separated String in java
- What is String in Java? String is a data type?
- What are different ways to create String Object?
- Write a method to check if input String is Palindrome?
- Write a method that will remove given character from the String?
- How can we make String upper case or lower case?
- What is String subSequence method?
- How to compare two Strings in java program?
- How to convert String to char and vice versa?
- How to convert String to byte array and vice versa?
- Can we use String in switch case?
- Write a program to print all permutations of String?
- Write a function to find out longest palindrome in a given string?
- Difference between String, StringBuffer and StringBuilder?
- Why String is immutable or final in Java
- How to Split String in java?
- Why Char array is preferred over String for storing password?
- How do you check if two Strings are equal in Java?
- What is String Pool?
- What does String intern() method do?
- Does String is thread-safe in Java?
- Why String is popular HashMap key in Java?
- String Programming Questions