enum

Author: HelloListen

effectivejava/Favorites.java

@@ -0,0 +1,274 @@
+package effectivejava;
+
+import java.util.EnumMap;
+import java.util.HashMap;
+import java.util.Map;
+
+/**
+ * Created by zhangbin on 16/2/3.
+ */
+public class Favorites {
+    private Map<Class<?>, Object> favorites = new HashMap<>();
+
+    public <T> void putFavorite(Class<T> type, T instance) {
+        if (type == null) {
+            throw new NullPointerException("Type is null");
+        }
+        favorites.put(type, type.cast(instance));
+    }
+
+    public <T> T getFavorite(Class<T> type) {
+        return type.cast(favorites.get(type));
+    }
+}
+
+enum Planet {
+    MERCURY(3.302e+23, 2.439e6),
+    VENUS(4.869e+24, 6.052e6),
+    EARTH(5.975e+24, 6.378e6),
+    MARS(6.419e+23, 3.393e6),
+    JUPITER(1.899e+27, 7.149e7),
+    SATURN(5.685e+26, 6.027e7),
+    URANUS(8.683e+25, 2.556e7),
+    NEPTUNE(1.024e+26, 2.477e7);
+    private final double mass;
+    private final double radius;
+    private final double surfaceGravity;
+
+    private static final double G = 6.67300E-11;
+
+    Planet(double mass, double radius) {
+        this.mass = mass;
+        this.radius = radius;
+        surfaceGravity = G * mass / (radius * radius);
+    }
+
+    public double mass() {
+        return mass;
+    }
+
+    public double radius() {
+        return radius;
+    }
+
+    public double surfaceWeight(double mass) {
+        return mass * surfaceGravity;
+    }
+
+    public double surfaceGravity() {
+        return surfaceGravity;
+    }
+}
+
+class WeightTable {
+    public static void main(String[] args) {
+        double earthWeight = Double.parseDouble(args[0]);
+        double mass = earthWeight / Planet.EARTH.surfaceGravity();
+        for (Planet p : Planet.values()) {
+            System.out.printf("Weight on %s is %f%n", p, p.surfaceWeight(mass));
+        }
+        double num = Operation.DIVIDE.apply(10, 20);
+        System.out.println(num);
+    }
+}
+
+enum Operation {
+    PLUS {
+        double apply(double x, double y) {
+            return x + y;
+        }
+    },
+    MINUS {
+        double apply(double x, double y) {
+            return x - y;
+        }
+    },
+    TIMES {
+        double apply(double x, double y) {
+            return x * y;
+        }
+    },
+    DIVIDE {
+        double apply(double x, double y) {
+            return x / y;
+        }
+    };
+
+    abstract double apply(double x, double y);
+}
+
+enum Operations {
+    PLUS("+") {
+        double apply(double x, double y) {
+            return x + y;
+        }
+    },
+    MINUS("-") {
+        double apply(double x, double y) {
+            return x - y;
+        }
+    },
+    TIMES("*") {
+        double apply(double x, double y) {
+            return x * y;
+        }
+    },
+    DIVIDE("/") {
+        double apply(double x, double y) {
+            return x / y;
+        }
+    };
+
+    private final String symbol;
+
+    Operations(String symbol) {
+        this.symbol = symbol;
+    }
+
+    @Override
+    public String toString() {
+        return symbol;
+    }
+
+    abstract double apply(double x, double y);
+
+    public static void main(String[] args) {
+        double x = Double.parseDouble(args[0]);
+        double y = Double.parseDouble(args[1]);
+        for (Operation op : Operation.values()) {
+            System.out.printf("%f %s %f = %f%n", x, op, y, op.apply(x, y));
+        }
+    }
+}
+
+enum PayrollDay {
+    MONDAY, TUESDAY, WEDNESDAY, THURSDAY, FRIDAY, SATURDAY, SUNDAY;
+    private static final int HOURS_PER_SHIFT = 8;
+
+    double pay(double hoursWorked, double payRate) {
+        double basePay = hoursWorked * payRate;
+        double overtimePay;
+        switch (this) {
+            case SATURDAY:
+            case SUNDAY:
+                overtimePay = hoursWorked * payRate / 2;
+                break;
+            default:
+                overtimePay = hoursWorked <= HOURS_PER_SHIFT ? 0 : (hoursWorked - HOURS_PER_SHIFT) * payRate / 2;
+                break;
+        }
+        return basePay + overtimePay;
+    }
+}
+
+enum PayrollDay2 {
+    MONDAY(PayType.WEEKDAY), TUESDAY(PayType.WEEKDAY),
+    WEDNESDAY(PayType.WEEKDAY), THURSDAY(PayType.WEEKDAY),
+    FRIDAY(PayType.WEEKDAY),
+    SATURDAY(PayType.WEEKEND), SUNDAY(PayType.WEEKEND);
+
+    private static final int HOURS_PER_SHIFT = 8;
+
+
+    private final PayType payType;
+
+    PayrollDay2(PayType payType) {
+        this.payType = payType;
+    }
+
+    double pay(double hoursWorked, double payRate) {
+        return payType.pay(hoursWorked, payRate);
+    }
+
+    private enum PayType {
+        WEEKDAY {
+            double overtimePay(double hours, double payRate) {
+                return hours <= HOURS_PER_SHIFT ? 0 : (hours - HOURS_PER_SHIFT) * payRate / 2;
+            }
+        },
+        WEEKEND {
+            double overtimePay(double hours, double payRate) {
+                return hours * payRate / 2;
+            }
+        };
+
+        abstract double overtimePay(double hours, double payRate);
+
+        double pay(double hoursWorked, double payRate) {
+            double basePay = hoursWorked * payRate;
+            return basePay + overtimePay(hoursWorked, payRate);
+        }
+    }
+}
+
+interface Operation1 {
+    double apply(double x, double y);
+}
+
+enum ExtendedOperation implements Operation1 {
+    EXP("^") {
+        public double apply(double x, double y) {
+            return Math.pow(x, y);
+        }
+    },
+    REMAINDER("%") {
+        public double apply(double x, double y) {
+            return x % y;
+        }
+    };
+    private final String symbol;
+
+    ExtendedOperation(String symbol) {
+        this.symbol = symbol;
+    }
+
+    @Override
+    public String toString() {
+        return symbol;
+    }
+
+    public static void main(String[] args) {
+        double x = Double.parseDouble(args[0]);
+        double y = Double.parseDouble(args[1]);
+        test(ExtendedOperation.class, x, y);
+    }
+
+    private static <T extends Enum<T> & Operation1> void test(Class<T> opSet, double x, double y) {
+        for (Operation1 op : opSet.getEnumConstants()) {
+            System.out.printf("%f %s %f = %f%n", x, op, y, op.apply(x, y));
+        }
+    }
+}
+
+enum Phase {
+    SOLID, LIQUID, GAS;
+
+    public enum Transition {
+        MELT(SOLID, LIQUID), FREEZE(LIQUID, SOLID),
+        BOIL(LIQUID, GAS), CONDENSE(GAS, LIQUID),
+        SUBLIME(SOLID, GAS), DEPOSIT(GAS, SOLID);
+
+        private final Phase src;
+        private final Phase dst;
+
+        Transition(Phase src, Phase dst) {
+            this.src = src;
+            this.dst = dst;
+        }
+
+        private static final Map<Phase, Map<Phase, Transition>> m = new EnumMap<>(Phase.class);
+
+        static {
+            for (Phase p : Phase.values()) {
+                m.put(p, new EnumMap<>(Phase.class));
+            }
+            for (Transition trans : Transition.values()) {
+                m.get(trans.src).put(trans.dst, trans);
+            }
+        }
+
+        public static Transition from(Phase src, Phase dst) {
+            return m.get(src).get(dst);
+        }
+    }
+}