Jagged Array in Java

A jagged array is a two-dimensional array where rows have different lengths. Java supports it naturally because a two-dimensional array is really an array of separate row arrays.

Why use a jagged array?

Use a rectangular array when every row has the same number of values. Use a jagged array when row sizes differ, such as the number of assignments completed by each student.

Allocating four slots for every student would leave unused cells. A jagged array represents the data without those empty values.

Create rows of different sizes

Run this example to see its output.

new int[3][] creates space for three row references, not three complete rows. Each row is created later with its own length. The nested loop uses the actual values in each row, so it works even when lengths differ.

Short initializer form

When all values are known, write the same jagged array more compactly:

Here, scores[0].length is 3, scores[1].length is 2, and scores[2].length is 4.

Safe traversal rule

Never use scores[0].length as the column limit for every row. It fails if another row is shorter. Use the current row length instead:

What to remember

• A jagged array is an array of rows with different lengths.
• Declare it with new int[rows][], then create each row separately.
• Use array[row].length during traversal.
• Choose jagged arrays when the data itself has uneven row sizes.