中间操作和终端操作
操作类型返回类型使用的类型/函数式接口函数描述符作用
filter中间Stream< T >Predicate< T>T->boolean筛选distinct中间Stream< T >T->boolean去重复skip中间Stream< T >longT->boolean跳过N个元素limit中间Stream< T >longT->boolean截取N个元素map中间Stream< R >Function< T,R >T->R映射flatMap中间Stream< R >Function< T,Stream< R > >T->Stream< R >扁平流映射sorted中间Stream< T >Comparator< T >(T,T)->int排序anyMatch终端booleanPredicate< T>T->boolean查找匹配noneMatch终端booleanPredicate< T>T->boolean查找匹配allMatch终端booleanPredicate< T>T->boolean查找匹配findAny终端Optional< T>查找匹配findFurst终端Optional< T>查找匹配forEach终端voidConsumer< T>T->void循环collect终端RCollector< T,A,R>返回listreduce终端booleanPredicate< T>(T,T)->T归纳总结count终端long返回集合大小
练习题
创建基础数据（实体类在下面）
Trader trader=new Trader("范冰冰","南昌");
Trader trader1=new Trader("金晨","南京");
Trader trader2=new Trader("林志玲","南昌");
Trader trader3=new Trader("江一燕","深圳");
List<Transaction> transactions=Arrays.asList(
new Transaction(trader,2011,300),
new Transaction(trader1,2012,1000),
new Transaction(trader2,2011,400),
new Transaction(trader3,2012,710),
new Transaction(trader2,2012,700),
new Transaction(trader1,2012,950)
);
练习题答案
System.out.println("2011年发生的所有交易，并按交易额排序（从低到高）："
+transactions.stream()
.filter(a>a.getYear()==2011)
.sorted(Comparator.comparing(Transaction::getValue)).collect(Collectors.toList()));
System.out.println("交易员都在那些不同的城市工作过："
+transactions.stream().map(o->o.getTrader().getCity())
.distinct().collect(Collectors.toList()));
System.out.println("所有来自南昌的交易员，并按姓名排序："
.map(o->o.getTrader().getName()).distinct().sorted().collect(Collectors.toList()));
System.out.println("返回所有交易员的姓名字符串，按首字母顺序排列："
.distinct().sorted().reduce("",(a,b)->a+" "+b));
System.out.println("有没有交易员是在南京工作的："
.map(Transaction::getTrader).findAny().get().getName());
System.out.println("打印生活在南昌的交易员的所有交易额--------------开始");
transactions.stream().filter(a->a.getTrader().getCity().equals("南昌"))
.forEach(a-> System.out.println(a.getTrader().getName()+" "+a.getValue()));
System.out.println("打印生活在南昌的交易员的所有交易额--------------结束");
System.out.println("所有交易中最高的交易额："
+transactions.stream().map(Transaction::getValue).reduce(Integer::max).get());
System.out.println("所有交易中最小的交易额："
+transactions.stream().map(Transaction::getValue).reduce(Integer::min).get());
public class Trader {
private String name;
private String city;
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 "交易员："+this.name+" 来自 "+this.city;
}
}
public class Transaction {
private Trader trader;
private int year;
private int value;
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 "{"+this.trader+", "+"时间："+this.year+", "+" 交易额："+this.value+"}";
}
}
