如何制作构造函数，如果有 2 个参数，则接受 2；如果有 3 个参数，则接受 3

Question

Java 新手...

我有一个名称类，其中包含：

private String firstName;
private String middleInitial;
private String lastName;

作为其实例变量。

如果我的某些数据只有firstName和lastName，没有middleInitial，我将如何创建构造函数，使其只需要2个参数而不是3个？

Answer 1

您只需编写一个具有两个参数的构造函数和一个具有三个

public YourClass(String firstName, String lastName) {
   ...
}

public YourClass(String firstName, String middleInitial, String lastName) {
    ...
}

调用者的构造函数，然后调用者就可以根据自己的需要选择使用适当的构造函数。

Answer 2

好吧，有两种选择：

• 只需拥有一个带有三个参数的构造函数，并使用 null 或 middleInitial 的空字符串来调用它。
• 重载构造函数，可能会调用另一个构造函数。

作为后者的示例，使用空字符串作为默认的中间名首字母：

public Person(String firstName, String middleInitial, String lastName)
{
    this.firstName = firstName;
    this.middleInitial = middleInitial;
    this.lastName = lastName;
}


public Person(String firstName, String lastName)
{
    this(firstName, "", lastName);
}

但是，编译器需要知道您正在从调用站点调用哪一个。所以你可以这样做：

new Person("Jon", "L", "Skeet");

或

new Person("Jon", "Skeet");

...但你不能这样做：

// Invalid
new Person(firstName, gotMiddleInitial ? middleInitial : ???, lastName);

并期望编译器决定使用“两个名称”变体。

Answer 3

在 Java 中，构造函数不能有默认参数。这里唯一的选择是编写两个构造函数。幸运的是，Java 允许您从其他构造函数调用构造函数。你可以这样做：

public class MyClass {
    private String firstName;
    private String middleInitial;
    private String lastName;

    public MyClass(String firstName, String middleInitial, String lastName) {
        this.firstName = firstName;
        this.middleInitial = middleInitial;
        this.lastName = lastName;
    }

    public MyClass(String firstName, String lastName) {
        this(firstName, "", lastName);
    }

    ...
}

Answer 4

public Class Name{
private String first;
private String middle;
private String last;

public Name(String first, String middle, String last){
this.first = first;
this.middle = middle;
this.last = last;
}

public Name(String first, String last){
this.first = first;
this.last = last;
}

}

Answer 5

您可以使用两个构造函数：

public Person(String firstName, String lastName)
{
    this(firstName, null, lastName);
}

public Person(String firstName, String middleInitial, String lastName)
{
    this.firstName     = firstName;
    this.middleInitial = middleInitial;
    this.lastName =    = lastName;
}

Answer 6

定义 2 个构造函数，一个有 2 个参数，一个有 3 个参数。

Answer 7

您可以编写两个构造函数。

public Person( String firstName, String lastName, String middleName ) { ... }

public Person( String firstName, String lastName ) { ... }

Answer 8

public void myBike(String name, String color)
{
      System.out.println("My bike's name is " + name + " and is " + color + ".");
}

public void myBike(String name, String color, float height)
{
      System.out.println("My bike's name is " + name + " and is " + color + ".");
      System.out.println("My bike is also " + height + " inches tall.");
}

Answer 9

建造者模式...

class Name {

            Builder builder;


            public String getSurname() {
                return builder.surname;
            }

            // getter...


            public Name(Builder builder) {
                this.builder = builder;
            }


            class Builder {

                String surname = "";
                String middleName = "";
                String name = "";


                Builder surname(String surname) {
                    this.surname = surname;
                    return this;
                }


                Builder middleName(String middleName) {
                    this.middleName = middleName;
                    return this;
                }


                Builder name(String name) {
                    this.name = name;
                    return this;
                }


                Name build() {
                    return new Name(this);
                }

            }
        }