Basic Java
String Questions and Answers:
1. What is a String in Java?
Answer: A String is a sequence of characters in Java. It's an object that represents a series of characters.
2. How do you create a String object in Java?
Answer: You
can create a String object using either the `String` class constructor or by
assigning a string literal enclosed in double quotes.
String Literal:
String_class variable_name =” Value”;
e.g., String name=” Rohan”;
Using new Keyword:
String_Class object=new String_class ();
e.g., String name=new String(“Rohan”);
3. What is the difference between `String` and
`StringBuilder` in Java?
Answer:
`String` objects are immutable (unchangeable), while `StringBuilder` allows for
mutable sequences of characters, making it more efficient for concatenation of
strings.
4. How do you
concatenate strings in Java?
Answer: Strings can
be concatenated in Java using the `+` operator or by using the `concat()`
method.
e.g.
String str1 = "Hello, ";
String str2 = "World!";
String result = str1.concat(str2); // result is
"Hello, World!"
String result = str1.concat(“India”); // result
is "Hello, India"
5. How can you compare two strings in Java?
Answer: You can
compare strings in Java using the `equals()` method for content comparison and
`==` for reference comparison.
e.g.
String str1 = "Hello";
String str2 = "Hello";
boolean isEqual = str1.equals(str2); // isEqual
is true
boolean isEqual = str1.equals(“hello”); //
isEqual is false
6. What is the
`StringBuffer` class in Java used for?
Answer:
`StringBuffer` is a thread-safe, mutable sequence of characters used for
manipulating strings. It's less efficient than `StringBuilder` but ensures
thread safety.
7. How do you
convert a String to uppercase in Java?
Answer: Use the `toUpperCase()` method to convert a String to uppercase in Java.
e.g.
String str =
"hello";
String upper = str.toUpperCase(); // upper is
"HELLO"
8. Explain the
`charAt()` method in Java String.
Answer: The
`charAt()` method returns the character at a specified index within a string.
Indexing starts at 0.
e.g.
String str = "Hello";
char ch = str.charAt(1); // ch is 'e'
9. What is the purpose
of the `length()` method in Java String?
Answer: The
`length()` method returns the length (number of characters) of a string.
e.g.
String str = "Hello, World!";
int length = str. length (); // length is 13
10. How can you
check if a string contains a specific character or substring in Java?
Answer: You
can use `contains()` to check if a string contains a specific substring and
`indexOf()` to check for a specific character or substring occurrence.
e.g.
String str = "Hello, World!";
boolean containsHello = str.contains("Hello");
// containsHello is true
11. How do you convert
an integer to a String in Java?
Answer: Use
the `String.valueOf()` method or concatenation with an empty string to convert
an integer to a String.
12. Explain the `substring()` method in Java.
Answer: The `substring()` method
extracts a portion of a string based on the specified beginning and ending
indices.
substring(int beginIndex)
e.g. String
str = "Hello, World!";
String substr = str.substring(7); // substr is
"World!"
substring(int beginIndex, int endIndex)
e.g. String str = "Hello, World!";
String substr = str.substring(7, 12); // substr
is "World"
13. Can you reverse a String in Java? If yes, how?
Answer: Yes, you can reverse a string in Java by using a loop, `StringBuilder`, or converting it to a character array.
14. What is the
purpose of the `trim()` method in Java String?
Answer: The
`trim()` method removes leading and trailing whitespace from a string.
e.g.
String original = " Hello, there! ";
String trimmed = original.trim();
System.out.println("Original String:
'" + original + "'");//14 charecter
System.out.println("Trimmed
String: '" + trimmed + "'");//12 character
15. How do you
split a String based on a specific delimiter in Java?
Answer: Use
the `split()` method, providing the delimiter as an argument, to split a string
into an array of substrings.
16. Explain the
concept of immutability in Java String.
Answer:
Immutability means once a string object is created, its value cannot be
changed. Any operation on a string returns a new string object.
17. How can you
convert a String to an array of characters in Java?
Answer: Use
the `toCharArray()` method to convert a String to an array of characters.
18. How do you check if a String is empty or null in Java?
Answer: Use
`isEmpty()` to check if a string is empty and `null` check to determine if it's
null.
19. Explain the
difference between `String`, `StringBuffer`, and `StringBuilder`.
Answer:
`String` is immutable, `StringBuffer` is thread-safe but less efficient, while
`StringBuilder` is not thread-safe but more efficient for string manipulation.
20. Can you convert a String to a numeric data type in Java?
Answer: Yes,
you can use methods like `Integer.parseInt()`, `Double.parseDouble()`, etc., to
convert a String to a numeric data type in Java.
.png)
.png)
0 Comments