Complete Java Interview Guide
Questions
What is the difference between `String`, `StringBuilder`, and `StringBuffer` in Java?
The Scenario
You are a backend engineer at a social media company. You are writing a new service that needs to do a lot of string manipulation. You are not sure whether to use String, StringBuilder, or StringBuffer.
The Challenge
Explain the difference between String, StringBuilder, and StringBuffer in Java. What are the pros and cons of each approach, and which one would you choose for this use case?
A junior engineer might think that they are interchangeable. They might not be aware of the difference in mutability or the performance implications of choosing one over the other.
A senior engineer would be able to provide a detailed explanation of the differences between `String`, `StringBuilder`, and `StringBuffer`. They would also be able to explain the trade-offs between each approach and would have a clear recommendation for which one to use in this use case.
Step 1: Understand the Key Differences
| Feature | String | StringBuilder | StringBuffer |
|---|---|---|---|
| Mutability | Immutable | Mutable | Mutable and thread-safe |
| Performance | Slow for string manipulation, because a new object is created each time. | Fast for string manipulation. | Slower than StringBuilder, due to the overhead of synchronization. |
| Use Cases | When you need a string that will not change. | When you need to do a lot of string manipulation in a single-threaded environment. | When you need to do a lot of string manipulation in a multi-threaded environment. |
Step 2: Choose the Right Tool for the Job
For our use case, we should use a StringBuilder. This is because we are doing a lot of string manipulation in a single-threaded environment.
Step 3: Code Examples
Here are some code examples that show the difference between the three approaches:
String:
String s = "hello";
s = s + " world";In this example, a new String object is created for each string concatenation.
StringBuilder:
StringBuilder sb = new StringBuilder("hello");
sb.append(" world");In this example, the StringBuilder object is modified in place, which is much more efficient.
StringBuffer:
StringBuffer sb = new StringBuffer("hello");
sb.append(" world");The StringBuffer class is similar to the StringBuilder class, but it is thread-safe.
Practice Question
You are writing a multi-threaded application and need to do a lot of string manipulation. Which of the following would be the most appropriate?