toString
- Java course
- Beginner
- Lesson 92/116
- 4 min
Learn to obtain a string with toString.
toString: getting the final text
When you are done, you turn the StringBuilder into a String with toString. This method does not change the builder's content; it returns a new String.
StringBuilder sb = new StringBuilder();
sb.append("Done");
String result = sb.toString();
// "Done"Most of the time println automatically calls toString; so printing works even if you do not write it explicitly. But to store in a variable or pass to another method, toString is required.
Reusing the builder
After finishing, you can take toString and keep using the builder. Because toString does not clear the builder; it just returns a copy String.
StringBuilder sb = new StringBuilder("A");
String a = sb.toString(); // "A"
sb.append("B");
String ab = sb.toString(); // "AB"If you want to start the builder over, you can write sb.setLength(0). This is cheaper than creating a new object; especially when you reset often in a loop.
Practice Turn step into text
Create a StringBuilder; append "Step ", "5" and " - done" with append. Store the result in a String variable using toString and print it with println.
Starter code
public class Main {
public static void main(String[] args) {
// Create a StringBuilder
// Append three parts
// Store in a String variable with toString and print
}
}Sample solution
StringBuilder sb = new StringBuilder();
sb.append("Step ");
sb.append("5");
sb.append(" - done");
String result = sb.toString();
System.out.println(result);Expected output
Step 5 - done
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 What happens if you print a StringBuilder with println?
- toString is called automatically; the content is printed Correct answer
- It throws an error
- The address is printed
- Only the first character
Explanation: println calls toString automatically.
2 Match scenario to approach
| Term | Meaning |
|---|---|
Concat 2 texts once |
String + |
100 appends in a loop |
StringBuilder |
Turn builder into String |
toString |
Flip the text |
reverse |
3 Fill in the blank: convert to String
StringBuilder sb = new StringBuilder("Done");
String result = sb.____();StringBuilder sb = new StringBuilder("Done");
String result = sb.toString();Explanation: sb.toString() returns a String.