Java8新特性_stream API 練習
阿新 • • 發佈:2019-01-25
equal nbsp cit 查找 port foreach test stream case
交易員類
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 + "]"; } }
//交易類
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() { returntrader; } 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 + "]"; } }
實例類
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年發生的所有交易, 並按交易額排序(從低到高) @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. 交易員都在哪些不同的城市工作過? @Test public void test2(){ transactions.stream() .map((t) -> t.getTrader().getCity()) .distinct() .forEach(System.out::println); } //3. 查找所有來自劍橋的交易員,並按姓名排序 @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. 返回所有交易員的姓名字符串,按字母順序排序 @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. 有沒有交易員是在米蘭工作的? @Test public void test5(){ boolean bl = transactions.stream() .anyMatch((t) -> t.getTrader().getCity().equals("Milan")); System.out.println(bl); } //6. 打印生活在劍橋的交易員的所有交易額 @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,最高的交易額是多少 @Test public void test7(){ Optional<Integer> max = transactions.stream() .map((t) -> t.getValue()) .max(Integer::compare); System.out.println(max.get()); } //8. 找到交易額最小的交易 @Test public void test8(){ Optional<Transaction> op = transactions.stream() .min((t1, t2) -> Integer.compare(t1.getValue(), t2.getValue())); System.out.println(op.get()); } }
Java8新特性_stream API 練習