2D Arrays: every key term you need

2D Arrays

Array of arrays; represents table/matrix. int[][] matrix = new int[rows][cols];. Access: matrix[i][j].

2D Array Initialization

int[][] matrix = {{1,2,3}, {4,5,6}};. Rows: matrix.length, columns: matrix[0].length (if rectangular).

2D Array Iteration

Nested loops: outer row, inner column. for(int i=0; i<matrix.length; i++) for(int j=0; j<matrix[i].length; j++).

Ragged Arrays

Each row different length. int[][] ragged = new int[3][]; ragged[0] = new int[2]; ragged[1] = new int[5];.

2D Array Algorithms

Row sum: sum column j for each i. Column sum: sum row i for each j. Diagonal: matrix[i][i]. Reverse: swap.

Matrix Operations

Addition: new[i][j] = a[i][j] + b[i][j]. Multiplication: complex (inner dimension must match).

Searching 2D Arrays

Linear search: nested loops checking each element. 2D index: track both i,j. Return found or not found.

2D Array Pass to Method

Method receives reference. Modifications affect original. Example: void fillMatrix(int[][] m) modifies array outside.

ArrayList of ArrayLists

ArrayList<ArrayList<Integer>> = dynamic 2D structure. Allows ragged dimensions. More flexibility than 2D array.

Unit 8 Summary

2D arrays represent tables/matrices. Nested loops iterate. Ragged arrays allow flexible dimensions. Support complex algorithms.

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