jdk8使用Lambda表达式

• 案例1

public class TestLambda1 {
	//原来的匿名内部类
	@Test
	public void test1(){
		Comparator<Integer> com = new Comparator<Integer>(){
			@Override
			public int compare(Integer o1, Integer o2) {
				return Integer.compare(o1, o2);
			}
		};
		TreeSet<Integer> ts = new TreeSet<>(com);
	}
	
	//现在的 Lambda 表达式
	@Test
	public void test2(){
		Comparator<Integer> com = (x, y) -> Integer.compare(x, y);
		TreeSet<Integer> ts = new TreeSet<>(com);
	}
 
}

• 案例2

# 实体类
public class Employee {
 
	private int id;
 
	private String name;
 
	private int age;
	
	private double salary;
 
	public Employee() {
	}
 
	public Employee(String name) {
		this.name = name;
	}
 
	public Employee(String name, int age) {
		this.name = name;
		this.age = age;
	}
 
	public Employee(int id, String name, int age, double salary) {
		this.id = id;
		this.name = name;
		this.age = age;
		this.salary = salary;
	}
 
	public int getId() {
		return id;
	}
 
	public void setId(int id) {
		this.id = id;
	}
 
	public String getName() {
		return name;
	}
 
	public void setName(String name) {
		this.name = name;
	}
 
	public int getAge() {
		return age;
	}
 
	public void setAge(int age) {
		this.age = age;
	}
 
	public double getSalary() {
		return salary;
	}
 
	public void setSalary(double salary) {
		this.salary = salary;
	}
 
	public String show() {
		return "测试方法引用！";
	}
 
	@Override
	public int hashCode() {
		final int prime = 31;
		int result = 1;
		result = prime * result + age;
		result = prime * result + id;
		result = prime * result + ((name == null) ? 0 : name.hashCode());
		long temp;
		temp = Double.doubleToLongBits(salary);
		result = prime * result + (int) (temp ^ (temp >>> 32));
		return result;
	}
 
	@Override
	public boolean equals(Object obj) {
		if (this == obj)
			return true;
		if (obj == null)
			return false;
		if (getClass() != obj.getClass())
			return false;
		Employee other = (Employee) obj;
		if (age != other.age)
			return false;
		if (id != other.id)
			return false;
		if (name == null) {
			if (other.name != null)
				return false;
		} else if (!name.equals(other.name))
			return false;
		if (Double.doubleToLongBits(salary) != Double.doubleToLongBits(other.salary))
			return false;
		return true;
	}
 
	@Override
	public String toString() {
		return "Employee [id=" + id + ", name=" + name + ", age=" + age + ", salary=" + salary + "]";
	}
 
}
 
public class TestLambda1 {
 
        # 创建集合
        List<Employee> emps = Arrays.asList(
        	new Employee(101, "张三", 18, 9999.99),
        	new Employee(102, "李四", 59, 6666.66),
        	new Employee(103, "王五", 28, 3333.33),
        	new Employee(104, "赵六", 8, 7777.77),
        	new Employee(105, "田七", 38, 5555.55)
        );
 
        //需求：获取公司中年龄小于 35 的员工信息
	public List<Employee> filterEmployeeAge(List<Employee> emps){
		List<Employee> list = new ArrayList<>();
		
		for (Employee emp : emps) {
			if(emp.getAge() <= 35){
				list.add(emp);
			}
		}
		
		return list;
	}
	
	@Test
	public void test3(){
		List<Employee> list = filterEmployeeAge(emps);
		for (Employee employee : list) {
			System.out.println(employee);
		}
	}
 
        //需求：获取公司中工资大于 5000 的员工信息
	public List<Employee> filterEmployeeSalary(List<Employee> emps){
		List<Employee> list = new ArrayList<>();
		for (Employee emp : emps) {
			if(emp.getSalary() >= 5000){
				list.add(emp);
			}
		}
		return list;
	}
 
	@Test
	public void test3(){
		List<Employee> list = filterEmployeeSalary(emps);
		for (Employee employee : list) {
			System.out.println(employee);
		}
	}
 
}

• 优化方式1：策略设计模式

# 接口
public interface MyPredicate<T> {
    public boolean test(T t);
}
 
# 实现类
public class FilterEmployeeForAge implements MyPredicate<Employee>{
	@Override
	public boolean test(Employee t) {
	    return t.getAge() <= 35;
	}
}
 
# 实现类
public class FilterEmployeeForSalary implements MyPredicate<Employee> {
	@Override
	public boolean test(Employee t) {
	    return t.getSalary() >= 5000;
	}
}
 
# 测试
public class TestLambda1 {
 
      public List<Employee> filterEmployee(List<Employee> emps, MyPredicate<Employee> mp){
		List<Employee> list = new ArrayList<>();
		for (Employee employee : emps) {
			if(mp.test(employee)){
				list.add(employee);
			}
		}
		return list;
	}
	
	@Test
	public void test4(){
		List<Employee> list = filterEmployee(emps, new FilterEmployeeForAge());
		for (Employee employee : list) {
			System.out.println(employee);
		}
		System.out.println("------------------------------------------");
		List<Employee> list2 = filterEmployee(emps, new FilterEmployeeForSalary());
		for (Employee employee : list2) {
			System.out.println(employee);
		}
	}
 
}

• 优化方式2：匿名内部类

# 接口
public interface MyPredicate<T> {
    public boolean test(T t);
}
 
# 测试
public class TestLambda1 {
 
      public List<Employee> filterEmployee(List<Employee> emps, MyPredicate<Employee> mp){
		List<Employee> list = new ArrayList<>();
		for (Employee employee : emps) {
			if(mp.test(employee)){
				list.add(employee);
			}
		}
		return list;
	}
	
	@Test
	public void test5(){
		List<Employee> list = filterEmployee(emps, new MyPredicate<Employee>() {
			@Override
			public boolean test(Employee t) {
				return t.getId() <= 103;
			}
		});
		for (Employee employee : list) {
			System.out.println(employee);
		}
	}
 
}

• 优化方式3：Lambda表达式

public class TestLambda1 {
 
      public List<Employee> filterEmployee(List<Employee> emps, MyPredicate<Employee> mp){
		List<Employee> list = new ArrayList<>();
		for (Employee employee : emps) {
			if(mp.test(employee)){
				list.add(employee);
			}
		}
		return list;
	}
	
	@Test
	public void test6(){
		List<Employee> list = filterEmployee(emps, (e) -> e.getAge() <= 35);
		list.forEach(System.out::println);
		System.out.println("------------------------------------------");
		List<Employee> list2 = filterEmployee(emps, (e) -> e.getSalary() >= 5000);
		list2.forEach(System.out::println);
	}
 
}

• 优化方式4：Stream API

public class TestLambda1 {
	@Test
	public void test7(){
		emps.stream()
			.filter((e) -> e.getAge() <= 35)
			.forEach(System.out::println);
		System.out.println("----------------------------------------------");
		emps.stream()
			.map(Employee::getName)
			.limit(3)
			.sorted()
			.forEach(System.out::println);
	}
}