Added methods to stock class:

- getHistoricalPrices: returns a list of all prices for a stock
- getHighestPrice: returns the highest historical price for a stock
- getLowestPrice: returns the lowest historical price for a stock
- getLatestPriceChange: returns the difference between the current and previous price for a stock

src/main/java/millions/Stock.java

@@ -29,4 +29,35 @@ public BigDecimal getSalesPrice() {
   public void addNewSalesPrice(BigDecimal price) {
     this.prices.add(price);
   }
+
+  public List<BigDecimal> getHistoricalPrices() {
+    return this.prices;
+  }
+
+  public BigDecimal getHighestPrice() {
+    BigDecimal highestPrice = this.prices.get(0);
+    for (BigDecimal price : this.prices) {
+      if (price.compareTo(highestPrice) > 0) {
+        highestPrice = price;
+      }
+    }
+    return highestPrice;
+  }
+
+  public BigDecimal getLowestPrice() {
+    BigDecimal lowestPrice = this.prices.get(0);
+    for (BigDecimal price : this.prices) {
+      if (price.compareTo(lowestPrice) < 0) {
+        lowestPrice = price;
+      }
+    }
+    return lowestPrice;
+  }
+
+  public BigDecimal getLatestPriceChange() {
+    BigDecimal currentPrice = this.prices.getLast();
+    BigDecimal lastPrice = this.prices.get(this.prices.size() - 2);
+
+    return currentPrice.subtract(lastPrice);
+  }
 }