package com.example.demo;
import lombok.Data;
import lombok.ToString;
import lombok.extern.log4j.Log4j2;
import one.util.streamex.StreamEx;
import org.junit.Test;
import java.util.Collection;
import java.util.Comparator;
import java.util.List;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;
import java.util.function.Function;
import java.util.function.Predicate;
import java.util.stream.Collectors;
import java.util.stream.LongStream;
import java.util.stream.Stream;
import static org.junit.Assert.assertEquals;
import static org.junit.Assert.assertTrue;
@Log4j2
public class EmployeeTestCase extends BaseTest{
@Test
public void distinct() {
//常規實現方式
List<Employee> employeesDis = list.stream().distinct().collect(Collectors.toList());
assertEquals(employeesDis.size(),5);
//StreamEx 實現方式
List<Employee> employeesDisBySalary2 = StreamEx.of(list).distinct(Employee::getSalary)
.peek(System.out::println).collect(Collectors.toList());
//Stream filter 實現方式
List<Employee> employeesDisBySalary = list.stream().filter(distinctByKey(Employee::getSalary))
.collect(Collectors.toList());
assertEquals(employeesDisBySalary,employeesDisBySalary2);
}
private static <T> Predicate<T> distinctByKey(Function<? super T, ?> keyExtractor) {
Map<Object,Boolean> seen = new ConcurrentHashMap<>();
return t -> seen.putIfAbsent(keyExtractor.apply(t), Boolean.TRUE) == null;
}
}
package com.example.demo;
import java.util.Arrays;
import java.util.List;
public class BaseTest {
protected static final List<Employee> list = Arrays.asList(
new Employee(1, "Alex", 1000),
new Employee(2, "Michael", 2000),
new Employee(3, "Jack", 1500),
new Employee(4, "Owen", 1500),
new Employee(5, "Denny", 2000));
protected static final List<List<Employee>> listFlat = Arrays.asList(
Arrays.asList(new Employee(1, "Alex", 1000),
new Employee(2, "Michael", 2000)),
Arrays.asList(new Employee(3, "Jack", 1500),
new Employee(4, "Owen", 1500)),
Arrays.asList(new Employee(5, "Denny", 2000)));
}