refactoring : mutable data - replace derived variable with query

refactoring/src/main/java/com/example/refactoring/_06_mutable_data/_21_replace_derived_variable_with_query/Discount.java

@@ -0,0 +1,20 @@
+package com.example.refactoring._06_mutable_data._21_replace_derived_variable_with_query;
+
+public class Discount {
+
+    private double discount;
+
+    private double baseTotal;
+
+    public Discount(double baseTotal) {
+        this.baseTotal = baseTotal;
+    }
+
+    public double getDiscountedTotal() {
+        return this.baseTotal - this.discount;
+    }
+
+    public void setDiscount(double number) {
+        this.discount = number;
+    }
+}

refactoring/src/main/java/com/example/refactoring/_06_mutable_data/_21_replace_derived_variable_with_query/ProductionPlan.java

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+package com.example.refactoring._06_mutable_data._21_replace_derived_variable_with_query;
+
+import java.util.ArrayList;
+import java.util.List;
+
+public class ProductionPlan {
+
+    private List<Double> adjustments = new ArrayList<>();
+
+    public void applyAdjustment(double adjustment) {
+        this.adjustments.add(adjustment);
+    }
+
+    public double getProduction() {
+        return this.adjustments.stream().mapToDouble(Double::valueOf).sum();
+    }
+}

refactoring/src/main/java/com/example/refactoring/_06_mutable_data/_21_replace_derived_variable_with_query/before/Discount.java

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+package com.example.refactoring._06_mutable_data._21_replace_derived_variable_with_query.before;
+
+public class Discount {
+
+    private double discountedTotal;
+    private double discount;
+
+    private double baseTotal;
+
+    public Discount(double baseTotal) {
+        this.baseTotal = baseTotal;
+    }
+
+    public double getDiscountedTotal() {
+        return this.discountedTotal;
+    }
+
+    public void setDiscount(double number) {
+        this.discount = number;
+        this.discountedTotal = this.baseTotal - this.discount;
+    }
+}

refactoring/src/main/java/com/example/refactoring/_06_mutable_data/_21_replace_derived_variable_with_query/before/ProductionPlan.java

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+package com.example.refactoring._06_mutable_data._21_replace_derived_variable_with_query.before;
+
+import java.util.ArrayList;
+import java.util.List;
+
+public class ProductionPlan {
+
+    private double production;
+    private List<Double> adjustments = new ArrayList<>();
+
+    public void applyAdjustment(double adjustment) {
+        this.adjustments.add(adjustment);
+        this.production += adjustment;
+    }
+
+    public double getProduction() {
+        return this.production;
+    }
+}

refactoring/src/test/java/com/example/refactoring/_06_mutable_data/_21_replace_derived_variable_with_query/DiscountTest.java

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+package com.example.refactoring._06_mutable_data._21_replace_derived_variable_with_query;
+
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+class DiscountTest {
+
+    @Test
+    void discount() {
+        Discount discount = new Discount(100);
+        assertEquals(100, discount.getDiscountedTotal());
+
+        discount.setDiscount(10);
+        assertEquals(90, discount.getDiscountedTotal());
+    }
+
+}

refactoring/src/test/java/com/example/refactoring/_06_mutable_data/_21_replace_derived_variable_with_query/ProductionPlanTest.java

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+package com.example.refactoring._06_mutable_data._21_replace_derived_variable_with_query;
+
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+class ProductionPlanTest {
+
+    @Test
+    void production() {
+        ProductionPlan productionPlan = new ProductionPlan();
+        productionPlan.applyAdjustment(10);
+        productionPlan.applyAdjustment(20);
+        assertEquals(30, productionPlan.getProduction());
+    }
+
+}