CODEWITHSUNDEEP
javalistmatrixarraylistcollections
billy
billy

Reputation: 1493

Trying to create a Matrix with ArrayList?

Trying to create a matrix object of generic type that has int columns, rows, and values. Note: The code below uses integer type to simplify.

Example output:

21  703   22   23   

3   3   13  13  6

Or 

   studone   studtwo  studthree

   studfour  studnine studten

   studran  studmoreran studplus

Attempt:

Here is the constructor:

private ArrayList<ArrayList<Integer>> matrixOne;

public Matrix(int rows, int columns) {

    this.rows = rows;
    this.columns = columns;

    matrixOne = new ArrayList<ArrayList<ArrayList>>();

    for(int i = 0; i < rows; i++) {
        matrixOne.add(new ArrayList<ArrayList>());
    }
    for(int j = 0; j < columns; j++)  {
        matrixOne.get(j).add(new ArrayList<Integer>()); 
    }

}

ISSUE: When trying to add value to a particular row/col, I get the following error in below method: The method add(int) is undefined for the type Integer

 // on method .add()      <-------- error
public void insert(int row, int column, int value) {
    matrixOne.get(row).get(column).add(value);
}

Upvotes: 1

Views: 1685

Answers (3)

zawhtut
zawhtut

Reputation: 8561

I would like to suggest you to use the dimensional array instead. Following is the simple implementation for transforming list(vector) to dimensional array. Inspired by R 's matrix(vec,nrow = 3,ncol = 3)

public static void main(String[] args){
    int[] vec = {2,3,4,5,6,7,8,9,10};
    toMatrix(vec,3,3);//parameters: vector(list),row of expected matrix,column of expected matrix
}
public static int[][] toMatrix(int[] vec,int row ,int col){
     int[][] matrix = new int[row][col]; 
        int vecIndex = 0;//list index to pop the data out from vector
        //Vector to matrix transformation
        for(int i=0;i<row;i++){
            for(int j=0;j<col;j++){
                if(vecIndex==vec.length) break;
                matrix[i][j] = vec[vecIndex++];//pop the vector value
            }
        }

        // Displaying the matrix, can ignore if not necessary
        for(int i=0;i<row;i++){ 
            for(int j=0;j<col;j++){              
                System.out.print(matrix[i][j] + "   ");
            }
            System.out.println();
         }
        return matrix;
}

Upvotes: 1

Bedir Yilmaz
Bedir Yilmaz

Reputation: 4083

You are shadowing your field 

private ArrayList<ArrayList<Integer>> matrixOne;

with

ArrayList<ArrayList<ArrayList>> matrixOne = new ArrayList<ArrayList<ArrayList>>();

which doesnt have any type other than ArrayList. Try this :

matrixOne = new ArrayList<ArrayList<Integer>>();

for shadowing a class variable

Upvotes: 1

Pavlo Plynko
Pavlo Plynko

Reputation: 586

Try this:

public void insert(int row, int column, int value) {
    matrixOne.get(row).add(column, value);
}

Upvotes: 0

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