Add toString() for matrices and numbers.

src/main/java/ee/ut/cs/gitlab/maikov/expressions/MatrixValue.java

@@ -73,4 +73,9 @@ public class MatrixValue extends Value {
             throw new InvalidMatrixException("Matrix value is not a square matrix");
         }
     }
+
+    @Override
+    public String toString() {
+        return matrix.toString();
+    }
 }

src/main/java/ee/ut/cs/gitlab/maikov/expressions/Number.java

@@ -59,4 +59,9 @@ public class Number extends Value {
     public Value absoluteValue() {
         return new Number(Math.abs(this.getNumber()));
     }
+
+    @Override
+    public String toString() {
+        return Double.toString(number);
+    }
 }

src/main/java/ee/ut/cs/gitlab/maikov/matrix/Matrix.java

@@ -107,4 +107,20 @@ public class Matrix {
     public double[] getElements() {
         return elements;
     }
+
+    @Override
+    public String toString() {
+        StringBuilder stringBuilder = new StringBuilder();
+        for (int row = 0; row < rows; row++) {
+            stringBuilder.append('[');
+            for (int col = 0; col < cols; col++) {
+                stringBuilder.append(this.get(row, col));
+                if (col != cols-1) {
+                    stringBuilder.append(',').append(' ');
+                }
+            }
+            stringBuilder.append(']').append('\n');
+        }
+        return stringBuilder.toString();
+    }
 }

src/test/java/MatrixTest.java

@@ -92,4 +92,15 @@ public class MatrixTest {
                 3, 7, 2,
                 4, 8, 1}, transpose.getElements());
     }
+
+    @Test
+    void testMatrixToString() {
+        Matrix matrix = new Matrix(4, 2, new double[]{
+                2, 9,
+                4, 3,
+                7, 8,
+                1, 5
+        });
+        assertEquals("[2.0, 9.0]\n[4.0, 3.0]\n[7.0, 8.0]\n[1.0, 5.0]\n", matrix.toString());
+    }
 }