Group and map to enum for
each group total
import java.util.Arrays;
import java.util.List;
import java.util.Map;
import java.util.Set;
import java.util.stream.Collectors;
public class Main
{
public static void main(String...args)
{
Map> o =
Food.menu.stream().collect(
Collectors.groupingBy(Food::getType, Collectors.mapping(
dish ->
{
if (dish.getCalories() <= 400)
return CaloricLevel.diet;
else if (dish.getCalories() <= 700)
return CaloricLevel.normal;
else
return CaloricLevel.fat; },
Collectors.toSet() )));
System.out.println(o);
}
}
enum CaloricLevel { Diet, NormaL, Fat }
enum Type { Meat, Fish, Other }
class Food {
private final String name;
private final boolean vegetarian;
private final int calories;
private final Type type;
public Food(String name, boolean vegetarian, int calories, Type type)
{
this.name = name;
this.vegetarian = vegetarian;
this.calories = calories;
this.type = type;
}
public String getName()
{
return name;
}
public boolean isVegetarian()
{
return vegetarian;
}
public int getCalories()
{
return calories;
}
public Type getType()
{
return type;
}
public String toString()
{
return name;
}
public static final List menu =
Arrays.asList( new Food("pork", false, 1800, Type.MEAT),
new Food("beef", false, 7100, Type.MEAT),
new Food("chicken", false, 1400, Type.MEAT),
new Food("french fries", true, 1530, Type.OTHER),
new Food("rice", true, 3510, Type.OTHER),
new Food("season fruit", true, 1120, Type.OTHER),
new Food("pizza", true, 5150, Type.OTHER),
new Food("prawns", false, 1400, Type.FISH),
new Food("salmon", false, 4150, Type.FISH));
}
Group by Food type
import java.util.Arrays;
import java.util.List;
import java.util.Map;
import java.util.stream.Collectors;
public class Main
{
public static void main(String...args)
{
Map> o = Food.menu.stream().collect(Collectors.groupingBy(Food::getType));
System.out.println(o);
}
}
enum Type { Meat, Fish, Other }
class Food {
private final String name;
private final boolean vegetarian;
private final int calories;
private final Type type;
public Food(String name, boolean vegetarian, int calories, Type type)
{
this.name = name;
this.vegetarian = vegetarian;
this.calories = calories;
this.type = type;
}
public String getName()
{
return name;
public boolean isVegetarian()
{
return vegetarian;
}
public int getCalories()
{
return calories;
}
public Type getType()
{
return type;
}
public String toString()
{
return name;
}
public static final List menu =
Arrays.asList( new Food("pork", false, 1800, Type.Meat),
new Food("beef", false, 7100, Type.Meat),
new Food("chicken", false, 1400, Type.Meat),
new Food("french fries", true, 1530, Type.Other),
new Food("rice", true, 3510, Type.Other),
new Food("season fruit", true, 1120, Type.Other),
new Food("pizza", true, 5150, Type.Other),
new Food("prawns", false, 1400, Type.Fish),
new Food("salmon", false, 4150, Type.Fish));
}
Group by one property
import java.util.Arrays;
import java.util.List;
import java.util.Map;
import java.util.stream.Collectors;
public class Main
{
public static void main(String...args)
{
List transactions = Arrays.asList( new Transaction(Currency.EUR, 1500.0),
new Transaction(Currency.USD, 2300.0),
new Transaction(Currency.GBP, 9900.0),
new Transaction(Currency.EUR, 1100.0),
new Transaction(Currency.JPY, 7800.0),
new Transaction(Currency.CHF, 6700.0),
new Transaction(Currency.EUR, 5600.0),
new Transaction(Currency.USD, 4500.0),
new Transaction(Currency.CHF, 3400.0),
new Transaction(Currency.GBP, 3200.0),
new Transaction(Currency.USD, 4600.0),
new Transaction(Currency.JPY, 5700.0),
new Transaction(Currency.EUR, 6800.0) );
Map> transactionsByCurrencies =
transactions.stream().collect(Collectors.groupingBy(Transaction::getCurrency));
System.out.println(transactionsByCurrencies);
}
}
class Transaction
{
private final Currency currency;
private final double value;
public Transaction(Currency currency, double value)
{
this.currency = currency;
this.value = value;
}
public Currency getCurrency()
{
return currency;
}
public double getValue()
{
return value;
}
public String toString()
{
return currency + " " + value;
}
}
enum Currency
{
Eur, usd, jpy, gbp, chf
}
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