Top Java String Interview Questions
In this video we covered Java String Interview Questions which are often asked in the interview.
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Following are the questions:
Q.1) How can you create a String in Java?
Using Literal:
String str1 = “Hello";
Using Constructor:
String str2 = new String(“Hello");
How many objects will be created in case of Constructor?
2 String objects
One in heap and one in String Pool
Q.2) How do you compare two strings in Java?
Use the `equals()` method to compare the content of two strings for equality:
String str1 = "Hello";
String str2 = "Hello";
boolean areEqual = str1 == str2; // true
String str3 = new String(“Hello”);
String str4 = new String(“Hello”);
boolean isEqual = str3.equals(str4); // true
Q.3) How can you concatenate strings efficiently?
Use the `StringBuilder` class for efficient string concatenation, especially when dealing with multiple concatenations:
StringBuilder sb = new StringBuilder();
sb.append("Hello").append(" ").append("World");
String result = sb.toString();
Q.4) How can you convert a string to uppercase/lowercase?
Use the `toUpperCase()` and `toLowerCase()` methods:
String original = "Hello World";
String upper = original.toUpperCase();
String lower = original.toLowerCase();
Q.5) Can you reverse a string in Java?
Yes, you can reverse a string using a loop or `StringBuilder`:
String original = "Hello";
String reversed = new StringBuilder(original).reverse().toString();
Q.6) What is the difference between `String`, `StringBuilder`, and `StringBuffer`?
`String`: Immutable, meaning the content cannot be changed after creation.
`StringBuilder`: Mutable and not thread-safe, suitable for single-threaded operations.
`StringBuffer`: Mutable and thread-safe, appropriate for multi-threaded operations.
Q.7)Explain the `substring()` method.
The `substring(int beginIndex)` method returns a new string that is a substring of the original string starting from the `beginIndex`.
Q.8) How do you check if a string contains a specific substring?
Use the `contains()` method:
String text = "Hello World";
boolean containsHello = text.contains("Hello");
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