matrix multiplication and sum

Class with methods:
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public class Matrix {

    public int size1, size2, size3, size4;
    public int[][] matrix1; int[][] matrix2; int[][] matrixendMulti; int[][] matrixendSum;

    Matrix()
    {
        size1=0;
        size2=0;
        size3=0;
        size4=0;

        matrix1=new int [size1][size2];
        matrix2=new int [size3][size4];
        matrixendMulti= new int [size1][size4];
        matrixendSum= new int[size1][size2];

    }

    Matrix(int size1, int size2, int size3, int size4, int K)
    {

            this.size1 = size1;
            this.size2 = size2;
            this.size3 = size3;
            this.size4 = size4;

            matrix1= new int [size1][size2];
            matrix2= new int [size3][size4];
            matrixendMulti= new int [size1][size4];
            matrixendSum = new int [size1][size2];

            for(int i=0; i< matrix1.length; i++)
            {

                for(int j=0; j<matrix1[0].length; j++)
                    matrix1[i][j] = (int) (Math.random()*K)+0;

            }

            for(int i=0; i< matrix2.length; i++)
            {
                for(int j=0; j<matrix2[0].length; j++)
                    matrix2[i][j] = (int) (Math.random()*K)+0;
            }
        }

    boolean checkMultiplication(int size2, int size3)
    {

        if(size2==size3)
            return true;

        return false;
    }

    boolean checkSum(int size1, int size2, int size3, int size4)
    {

        if(size1==size3 && size2==size4)
            return true;

        return false;

    }


  private void multiplication()
   {

           for (int i = 0; i < matrix1.length; i++)
           {
               for (int j = 0; j < matrix1.length; j++)
               {
                   matrixendMulti[i][j]=0;

                   for (int k = 0; k < matrix1[0].length; k++)

                       matrixendMulti[i][j] += matrix1[i][k] * matrix2[k][j];
               }

           }
   }

    void displayMultiplication()
    {
        if(checkMultiplication(size2, size3))
        {

        multiplication();

            System.out.println("Multiplication:");

            for (int i = 0; i < matrixendMulti.length; i++)
            {
                System.out.println();

                for (int j = 0; j < matrixendMulti[0].length; j++)
                    System.out.print(matrixendMulti[i][j]+" ");
            }
        }
              else
        System.out.println("The multiplication is not possible");

    }

    private void sum()
    {

        for(int i=0; i<matrixendSum.length; i++)
        {
            for(int j=0; j<matrixendSum[0].length; j++)
                matrixendSum[i][j]+=matrix1[i][j] + matrix2[i][j];

        }

    }

    void displaySum()
    {
        if(checkSum(size1, size2, size3, size4))
        {
            sum();

            System.out.println("Sum:");

            for(int i=0; i<matrixendSum.length; i++)
            {
                System.out.println();

                for(int j=0; j<matrixendSum[0].length; j++)
                    System.out.print(matrixendSum[i][j]+" ");

            }
        }
        else
            System.out.println("Addition is not possible");
    }
}
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Class with tester:
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import java.util.Scanner;

public class MatrixTester {
    public static void main(String[] args)
    {
        Scanner input = new Scanner(System.in);

        int size1, size2, size3, size4, K;

        System.out.println("Enter the dimensions of the first matrix");
        size1=input.nextInt();
        size2=input.nextInt();

        System.out.println("Enter the dimensions of the second matrix");
        size3=input.nextInt();
        size4=input.nextInt();

        System.out.println("Enter the maximum numbers on the matrix");
        K=input.nextInt();

        Matrix test = new Matrix(size1, size2, size3, size4, K);
        test.displayMultiplication();
        test.displaySum();
    }
}