用lambda表达式中的参数调用构造函数[重复]

Question

public class Employee {

    private Long id;
    private String name;
    private String externalId;

    public Employee(Long id, String name, String externalId) {
        this.id = id;
        this.name = name;
        this.externalId = externalId;
    }

    //getters, setter
}

private void performEmployeeProcessing() {
    Long employeeId = 2L;
    Object o = Optional.ofNullable(employeeService.getById(employeeId))
        .orElseGet(Employee::new, 1L, "", "");

    System.out.println(o);
}

上面写着编译错误

Employee::new、1L、“”、“
无法解析构造函数。

Answer 1

使用供应商:

.orElseGet(() -> new Employee( 1L, "", ""));

仅供参考，Employee实例仅在实际需要时才会创建。

如果构造函数没有arg，则可以使用方法引用employee::new。如果创建工厂方法，则仍然可以使用方法引用：

class Employee {
    // rest of class
    public static Employee createDummy() {
        return new Employee( 1L, "", "");
    }
}

.orElseGet(Employee::createDummy);