Filled out remaining functionality in SaleCalculator

src/main/java/temppackage/calculators/SaleCalculator.java

@@ -1,14 +1,37 @@
 package temppackage.calculators;
 
 import java.math.BigDecimal;
+import java.math.RoundingMode;
+
 import temppackage.Share;
 
-public class SaleCalculator {
+public class SaleCalculator implements TransactionCalculator{
   BigDecimal purchasePrice;
   BigDecimal salesPrice;
   BigDecimal quantity;
   public SaleCalculator(Share share) {
     super();
     this.purchasePrice = share.getPurchasePrice();
   }
+  @Override
+  public BigDecimal calculateGross() {
+    return salesPrice.multiply(quantity);
+  }
+
+  @Override
+  public BigDecimal calculateComission() {
+    return this.calculateGross().divide(new BigDecimal("100"), RoundingMode.HALF_UP);
+  }
+
+  @Override
+  public BigDecimal calculateTax() {
+    BigDecimal purchaseCosts = this.purchasePrice.multiply(this.quantity);
+    BigDecimal earnings = this.calculateGross().subtract(this.calculateComission()).subtract(purchaseCosts);
+    return earnings.multiply(new BigDecimal("30")).divide(new BigDecimal("100"), RoundingMode.HALF_UP);
+  }
+
+  @Override
+  public BigDecimal calculateTotal() {
+    return this.calculateGross().subtract(this.calculateComission()).subtract(this.calculateTax());
+  }
 }