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Java8新特性_stream API 练习
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交易员类
public class Trader {
private String name;
private String city;
public Trader() {
}
public Trader(String name, String city) {
this.name = name;
this.city = city;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getCity() {
return city;
}
public void setCity(String city) {
this.city = city;
}
@Override
public String toString() {
return "Trader [name=" + name + ", city=" + city + "]";
}
}
//交易类
public class Transaction {
private Trader trader;
private int year;
private int value;
public Transaction() {
}
public Transaction(Trader trader, int year, int value) {
this.trader = trader;
this.year = year;
this.value = value;
}
public Trader getTrader() {
return trader;
}
public void setTrader(Trader trader) {
this.trader = trader;
}
public int getYear() {
return year;
}
public void setYear(int year) {
this.year = year;
}
public int getValue() {
return value;
}
public void setValue(int value) {
this.value = value;
}
@Override
public String toString() {
return "Transaction [trader=" + trader + ", year=" + year + ", value="
+ value + "]";
}
}
实例类
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.Optional;
import java.util.stream.Stream; import org.junit.Before;
import org.junit.Test; public class TestTransaction { List<Transaction> transactions = null; @Before
public void before(){
Trader raoul = new Trader("Raoul", "Cambridge");
Trader mario = new Trader("Mario", "Milan");
Trader alan = new Trader("Alan", "Cambridge");
Trader brian = new Trader("Brian", "Cambridge"); transactions = Arrays.asList(
new Transaction(brian, 2011, 300),
new Transaction(raoul, 2012, 1000),
new Transaction(raoul, 2011, 400),
new Transaction(mario, 2012, 710),
new Transaction(mario, 2012, 700),
new Transaction(alan, 2012, 950)
);
} //1. 找出2011年发生的所有交易， 并按交易额排序（从低到高）
@Test
public void test1(){
transactions.stream()
.filter((t) -> t.getYear() == 2011)
.sorted((t1, t2) -> Integer.compare(t1.getValue(), t2.getValue()))
.forEach(System.out::println);
} //2. 交易员都在哪些不同的城市工作过？
@Test
public void test2(){
transactions.stream()
.map((t) -> t.getTrader().getCity())
.distinct()
.forEach(System.out::println);
} //3. 查找所有来自剑桥的交易员，并按姓名排序
@Test
public void test3(){
transactions.stream()
.filter((t) -> t.getTrader().getCity().equals("Cambridge"))
.map(Transaction::getTrader)
.sorted((t1, t2) -> t1.getName().compareTo(t2.getName()))
.distinct()
.forEach(System.out::println);
} //4. 返回所有交易员的姓名字符串，按字母顺序排序
@Test
public void test4(){
transactions.stream()
.map((t) -> t.getTrader().getName())
.sorted()
.forEach(System.out::println); System.out.println("-----------------------------------"); String str = transactions.stream()
.map((t) -> t.getTrader().getName())
.sorted()
.reduce("", String::concat); System.out.println(str); System.out.println("------------------------------------"); transactions.stream()
.map((t) -> t.getTrader().getName())
.flatMap(TestTransaction::filterCharacter)
.sorted((s1, s2) -> s1.compareToIgnoreCase(s2))
.forEach(System.out::print);
} public static Stream<String> filterCharacter(String str){
List<String> list = new ArrayList<>(); for (Character ch : str.toCharArray()) {
list.add(ch.toString());
} return list.stream();
} //5. 有没有交易员是在米兰工作的？
@Test
public void test5(){
boolean bl = transactions.stream()
.anyMatch((t) -> t.getTrader().getCity().equals("Milan")); System.out.println(bl);
} //6. 打印生活在剑桥的交易员的所有交易额
@Test
public void test6(){
Optional<Integer> sum = transactions.stream()
.filter((e) -> e.getTrader().getCity().equals("Cambridge"))
.map(Transaction::getValue)
.reduce(Integer::sum); System.out.println(sum.get());
} //7. 所有交易中，最高的交易额是多少
@Test
public void test7(){
Optional<Integer> max = transactions.stream()
.map((t) -> t.getValue())
.max(Integer::compare); System.out.println(max.get());
} //8. 找到交易额最小的交易
@Test
public void test8(){
Optional<Transaction> op = transactions.stream()
.min((t1, t2) -> Integer.compare(t1.getValue(), t2.getValue())); System.out.println(op.get());
} }
