java如何在同一行上实例化对象和调用setter？

Question

如果我有一个带有默认构造函数的Employee类：

private String firstName;
public Employee(){}

还有一个二传手：

public void setFirstName(String firstName){
    this.firstName = firstName;
}

为什么这一尝试未能在同一行中实例化和调用setter

Employee employee = new Employee().setFirstName("John");

Answer 1

应该是这样的：

Employee employee = new Employee();
employee.setFirstName("John");

Answer 2

因为setFirstName不返回任何内容。如果要链接方法，那么setFirstName必须返回Employee

另一种方法是使用以firstName为参数的构造函数

Answer 3

虽然这有点过头了，但您可以尝试使用builder pattern

public class Employee{
    private String firstName;

    public static class Builder{
        private String firstName;

        public Builder firstName(String firstName){
            this.firstName = firstName;
            return this;
        }

        public Employee build(){
            return new Employee(this);
        }
    }

    private Employee(Builder builder){
        firstName = builder.firstName;
    }
}

然后你可以做以下事情

Employee e = new Employee.Builder().firstName("John").build();