JMatrix stuff

genericUtils.TypeParameter.java

package genericUtils;

public abstract class TypeParameter<T> {
    abstract public Class<? extends T> getType();
    abstract public <S extends T> void useType(Class<S> type);
    
    public TypeParameter() {
        useType(getType());
    }
}

integers._N.java

package integers;

public interface _N extends _N0 {
    final static Object[] nums = new Object[] 
            {/*_0.class,*/ _1.class, _2.class, _3.class, _4.class, _5.class,
             _6.class, _7.class, _8.class, _9.class, _10.class, _11.class};
    
    public static int valueOf(Class<? extends _N> num) {
        for (int n = 0; n < nums.length; n++) {
            if (nums[n] == num) {
                return n + 1;
            }
        }
        
        throw new RuntimeException("this number does not exist.");
    }
    
    @SuppressWarnings("unchecked")
    public static Class<? extends _N> fromValue(int value) {
        return (Class<? extends _N>) nums[value - 1];
    }
}

Matrix.java

import integers.*;

public interface Matrix<N extends _N, M extends _N> {
    public double getElementAt(int x, int y);
    public void setElementAt(int x, int y, double value);
    public int numRows();
    public int numCols();
    
    public default String asString() {
        final String nl = System.getProperty("line.separator");
        String str = "[" + nl;
        for (int y = 0; y < numRows(); y++) {
            str += " [ ";
            for (int x = 0; x < numCols(); x++) {
                str += getElementAt(x, y) + " ";
            }
            str += "]" + nl;
        }
        return str + "]";
    }
    
    @SuppressWarnings("unchecked")
    public default Class<N> rows() {
        return (Class<N>) _N.fromValue(numRows());
    }
    
    @SuppressWarnings("unchecked")
    public default Class<M> cols() {
        return (Class<M>) _N.fromValue(numCols());
    }
    
    public default Matrix<N, M> add(Matrix<N, M> other) {
        Matrix<N, M> m = make(rows(), cols());
        for (int y = 0; y < numRows(); y++) {
            for (int x = 0; x < numCols(); x++) {
                m.setElementAt(x, y, getElementAt(x, y) + other.getElementAt(x, y));
            }
        }
        return m;
    }
    
    public default Matrix<N, M> multiply(double factor) {
        Matrix<N, M> m = make(rows(), cols());
        for (int y = 0; y < numRows(); y++) {
            for (int x = 0; x < numCols(); x++) {
                m.setElementAt(x, y, factor * getElementAt(x, y));
            }
        }
        return m;
    }
    
    public default <P extends _N> Matrix<N, P> multiply(Matrix<M, P> other) {
        Matrix<N, P> m = make(rows(), other.cols());
        for (int y = 0; y < numRows(); y++) {
            for (int x = 0; x < other.numCols(); x++) {
                double sum = 0;
                
                for (int i = 0; i < numCols(); i++) {
                    sum += getElementAt(i, y) * other.getElementAt(x, i);
                }
                
                m.setElementAt(x, y, sum);
            }
        }
        return m;
    }

    public default <P extends _N, Q extends _N> Matrix<P, Q> crop(Class<P> r, Class<Q> c) {
        return identity(r, rows()).multiply(this).multiply(identity(cols(), c));
    }
    
    public static <Rows extends _N, Cols extends _N> Matrix<Rows, Cols> make(Class<Rows> r, Class<Cols> c) {
        return new ArrayMatrix<Rows, Cols>(r, c);
    }    
    
    public static <Rows extends _N, Cols extends _N> Matrix<Rows, Cols> identity(Class<Rows> r, Class<Cols> c) {
        Matrix<Rows, Cols> m = make(r, c);
        for (int i = 0; i < Math.min(m.numRows(), m.numCols()); i++) {
            m.setElementAt(i, i, 1);
        }
        return m;
    }
    
    public class ArrayMatrix<Rows extends _N, Cols extends _N> implements Matrix<Rows, Cols> {
        private double[][] values;
        private final int rows, cols;
        
        ArrayMatrix(Class<Rows> r, Class<Cols> c) {
            rows = _N.valueOf(r);
            cols = _N.valueOf(c);
            values = new double[rows][cols];
        }
        
        public double getElementAt(int x, int y) {
            return values[y][x];
        }
        
        public void setElementAt(int x, int y, double value) {
            values[y][x] = value;
        }
        
        public int numRows() {
            return rows;
        }
        
        public int numCols() {
            return cols;
        }
    }
}

MatrixTest.java

import integers.*;
import genericUtils.TypeParameter;

public class MatrixTest {
    public static void main(String[] args) {
        Matrix<_2, _3> m23 = Matrix.make(_2.class, _3.class);
        for (int x = 0; x < 3; x++) {
            for (int y = 0; y < 2; y++) {
                m23.setElementAt(x, y, x + 2*y);
            }
        }
        
        System.out.println("0: " + m23.asString());
        System.out.println("1: " + m23.crop(_1.class, _2.class).asString());
        System.out.println("2: " + m23.crop(_5.class, _7.class).asString());
        
        System.out.println("3: " + m23.multiply(2).asString());
        
        Matrix<_3, _2> m32 = Matrix.make(_3.class, _2.class);
        for (int x = 0; x < 2; x++) {
            for (int y = 0; y < 3; y++) {
                m32.setElementAt(x, y, 2 + x);
            }
        }
        
        System.out.println("4: " + m23.multiply(m32).asString());
        //Matrix.make(_3.class, _5.class).multiply(m23) //Compiletime error
        System.out.println("5: " + Matrix.make(_3.class, _5.class).asString());
        
        int n = 3;

        new TypeParameter<_N>() {
            public Class<? extends _N> getType() {
                return _N.fromValue(n);
            }
            
            public <T extends _N> void useType(Class<T> three) {
                Matrix<_7, T> m73 = Matrix.make(_7.class, three);
                Matrix<_7, _4> m74 = m73.multiply(Matrix.make(three, _4.class));
                System.out.println("6: " + m74.asString());
            }
        };
    }

output.txt

0: [
 [ 0.0 1.0 2.0 ]
 [ 2.0 3.0 4.0 ]
]
1: [
 [ 0.0 1.0 ]
]
2: [
 [ 0.0 1.0 2.0 0.0 0.0 0.0 0.0 ]
 [ 2.0 3.0 4.0 0.0 0.0 0.0 0.0 ]
 [ 0.0 0.0 0.0 0.0 0.0 0.0 0.0 ]
 [ 0.0 0.0 0.0 0.0 0.0 0.0 0.0 ]
 [ 0.0 0.0 0.0 0.0 0.0 0.0 0.0 ]
]
3: [
 [ 0.0 2.0 4.0 ]
 [ 4.0 6.0 8.0 ]
]
4: [
 [ 6.0 9.0 ]
 [ 18.0 27.0 ]
]
5: [
 [ 0.0 0.0 0.0 0.0 0.0 ]
 [ 0.0 0.0 0.0 0.0 0.0 ]
 [ 0.0 0.0 0.0 0.0 0.0 ]
]
6: [
 [ 0.0 0.0 0.0 0.0 ]
 [ 0.0 0.0 0.0 0.0 ]
 [ 0.0 0.0 0.0 0.0 ]
 [ 0.0 0.0 0.0 0.0 ]
 [ 0.0 0.0 0.0 0.0 ]
 [ 0.0 0.0 0.0 0.0 ]
 [ 0.0 0.0 0.0 0.0 ]
]