[英]How to access a inner class through an outer class constructor?
我正在尝试使用我的 main 中的 person 构造函数和代码创建一个人
Person outerClass = new Person("Anon", new Date(06,03,1991), null);
但它说它找不到类日期。 我是否正确填写了这个构造函数并调用了类间?
public class Person implements Cloneable
{
private String name;
private Date born;
private Date died;//null indicates still alive.
public Person(String initialName, Date birthDate, Date deathDate)
{
if (consistent(birthDate, deathDate))
{
name = initialName;
born = new Date(birthDate);
if (deathDate == null)
died = null;
else
died = new Date(deathDate);
}
else
{
System.out.println("Inconsistent dates. Aborting.");
System.exit(0);
}
}
private class Date
{
private String month;
private int day;
private int year; //a four digit number.
public Date( )
{
month = "January";
day = 1;
year = 1000;
}
public Date(int monthInt, int day, int year)
{
setDate(monthInt, day, year);
}
既然您的需求需要内部类,那么让我们暂且搁置有关Date
是否适合作为Person
的内部类的问题。
它找不到类Date
因为它是私有的。 然而,即使它是公开的,您仍然无法实例化一个,因为您首先需要一个Person
的实例。 一种方法是从构造函数中删除Date
参数并改用修改器。 例如:
public class Person {
private final String name;
private Date birthDate;
public class Date {
private final int year, month, day;
public Date(final int year, final int month, final int day) {
this.year = year;
this.month = month;
this.day = day;
}
public String toString() {
// look at me, I can access attributes of the enclosing Person
return name + " is associated with the year " + year;
}
}
public Person(final String name) {
this.name = name;
}
public void setBirthDate(final Date birthDate) {
this.birthDate = birthDate;
}
public static final void main(final String... arguments) throws Exception {
final Person person = new Person("name");
final Date birthDate = person.new Date(2015, 11, 9);
person.setBirthDate(birthDate);
}
}
但是,如果内部类独立于外部类的实例存在是有意义的,那么它应该是静态的。 这将允许您在没有现有Person
的情况下自行实例化Date
。 例如:
public class Person {
private final String name;
private final Date birthDate;
public static class Date {
private final int year, month, day;
public Date(final int year, final int month, final int day) {
this.year = year;
this.month = month;
this.day = day;
}
public String toString() {
// I do not know about any Person
return "year: " + year;
}
}
public Person(final String name, final Date birthDate) {
this.name = name;
this.birthDate = birthDate;
}
public static final void main(final String... arguments) throws Exception {
final Person person = new Person("name", new Date(2015, 11, 9));
}
}
请注意,这在功能上与将Date
声明为其自己的顶级类相同,只是现在完全限定的类名称以“Person.Date”结尾。
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