insert and delete

Learn to edit text with insert and delete.

insert and delete

With insert you add content at a specific index, and with delete you remove a range. These methods modify the StringBuilder in place.

StringBuilder sb = new StringBuilder("Merhaba");
sb.insert(0, "Selam ");
// "Selam Merhaba"
sb.delete(0, 6);
// "Merhaba"

insert shifts the second parameter to the first index; the rest moves right. delete(start, end) removes the range with start inclusive and end exclusive.

Prepend with insert

The most common insert example is prepending content. insert(0, ...) does that.

StringBuilder sb = new StringBuilder("world");
sb.insert(0, "Hello ");
// "Hello world"

Here insert(0, ...) puts the new content at the very front; the existing "world" shifts right. This is much more efficient than String when you need to prepend repeatedly.

Exercise Insert a heading and clean up

Start a StringBuilder with "Monthly Report". Use insert(0, "--- ") to add dashes at the front. Then use delete(0, 4) to remove those dashes. Print the result with toString.

Show example solution

StringBuilder sb = new StringBuilder("Monthly Report");
sb.insert(0, "--- ");
sb.delete(0, 4);
System.out.println(sb.toString());

Test yourself

What does sb.delete(1, 3) do?
- Removes indices 1 and 2
- Removes indices 1 and 3
- Removes from index 1 to 3 (3 inclusive)
- Removes the third character
Show answer

Removes from index 1 to 3 (3 inclusive) — delete(start, end) is start inclusive, end exclusive.
Match call to result

insert(0, "X")

Prepends X
insert(3, "X")

Inserts X at index 3
delete(0, 2)

Removes the first two chars
delete(1, 1)

Removes nothing

Fill in the blank: prepend

StringBuilder sb = new StringBuilder("world");
sb.____(0, "Hello ");

Show answer

StringBuilder sb = new StringBuilder("world");
sb.insert(0, "Hello ");

Next lesson: reverse

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