Summary - String builder

Combine append, insert and reverse to write a report generator.

Summary: String builder

In this group you saw the core methods of StringBuilder: append, insert, delete, reverse and toString.

They change the text in place; that is why loop concatenation is much more efficient than String +. You take the final String with toString.

Now you will combine these to write a small report generator: you will join lines in a loop and emit the output with toString.

Exercise Report generator

Create a StringBuilder. In a loop from 1 to 3, for each number call append("Line "), append(i) and append("\n"). After the loop, print the result with toString.

Show example solution

StringBuilder sb = new StringBuilder();
for (int i = 1; i <= 3; i++) {
  sb.append("Line ");
  sb.append(i);
  sb.append("\n");
}
System.out.println(sb.toString());

Test yourself

When is StringBuilder preferred over String +?
- Many concatenations inside a loop
- A simple one-line concat
- Writing a fixed text
- Never
Show answer

A simple one-line concat — In a loop, StringBuilder is much more efficient.
Match method to purpose

append

Adds at the end
insert

Adds at an index
delete

Removes a range
reverse

Flips the text

Fill in the blank: reset the builder

StringBuilder sb = new StringBuilder("old");
sb.____(0);

Show answer

StringBuilder sb = new StringBuilder("old");
sb.setLength(0);

Next lesson: Scanner

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