Stream API练习实例

落日映苍穹つ 2023-01-14 13:58 185阅读 0赞

### 文章目录 ###

*  1、实体类
 *  2、实例

# 1、实体类 #

交易员类

//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

//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 + "]";
    	}
    
    }

# 2、实例 #

测试数据

List<Transaction> transactions = null;
    	
    		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、给定一个数字列表，返回一个由每个数的平方构成的列表**

@Test
    	public void test1(){ 
    		Integer[] nums = new Integer[]{ 1,2,3,4,5};
    		
    		Arrays.stream(nums)
    			  .map((x) -> x * x)
    			  .forEach(System.out::println);
    	}

![在这里插入图片描述][20210420204451266.png]  
**2、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);
    	}

![在这里插入图片描述][20210420204634447.png]  
**3、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);
    	}

![在这里插入图片描述][20210420204724559.png]  
**4、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);
    	}

![在这里插入图片描述][20210420204800449.png]  
**5、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);
    	}

![在这里插入图片描述][20210420204844846.png]  
**6、是否有在米兰工作的交易员**

@Test
    	public void test5(){ 
    		boolean bl = transactions.stream()
    					.anyMatch((t) -> t.getTrader().getCity().equals("Milan"));
    		
    		System.out.println(bl);
    	}

![在这里插入图片描述][2021042020493033.png]  
**7、打印生活在剑桥的交易员的所有交易额**

@Test
    	public void test6(){ 
    		//1
    		Optional<Integer> sum = transactions.stream()
    					.filter((e) -> e.getTrader().getCity().equals("Cambridge"))
    					.map(Transaction::getValue)
    					.reduce(Integer::sum);
    		
    		System.out.println(sum.get());
    		//2
    		Integer test = transactions.stream()
    				.filter((e) -> e.getTrader().getCity().equals("Cambridge"))
    				.collect(Collectors.summingInt(Transaction::getValue));
    		System.out.println(test);
    	}

![在这里插入图片描述][20210420205012702.png]  
**8、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());
    	}

![在这里插入图片描述][20210420205041850.png]  
**9、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());
    	}

![在这里插入图片描述][2021042020512276.png]

[20210420204451266.png]: /images/20221022/63541b48cb06418fbafb0b1f24e92e72.png
[20210420204634447.png]: /images/20221022/214f8b4bc9cb4962a6c6efd1bd009ac8.png
[20210420204724559.png]: /images/20221022/46d0df8eb1514d2c82961b8dba025861.png
[20210420204800449.png]: /images/20221022/6d8f1e62f2164169a34c128677e79802.png
[20210420204844846.png]: /images/20221022/ebfcaf7a8cb44f539c1a48a916cc6646.png
[2021042020493033.png]: /images/20221022/042df8e366ca4702b7546436ba908b2b.png
[20210420205012702.png]: /images/20221022/fac796cceb364309a7a7df400beebe33.png
[20210420205041850.png]: /images/20221022/9e5a025de5824c168eeb72eff04da865.png
[2021042020512276.png]: /images/20221022/d606cab4105b4925856835dbce744a12.png