更新:我可以将变量更改为私有,静态或最终变量。
我有一个父班和一个子班。我想重用 父级类中的方法。通常,这就像super.methodFromParentClass()
一样简单,您已完成。 但是,当我这样做时,我想重用的方法是使用来自父类的实例变量数据>错误,或更确切地说,我 不 想要这种行为。我在子类中有 DIFFERENT 初始化数据,这些数据需要传递到要重用的方法中。如果您查看我想重用的方法(下面只是一个简单的示例,但是想法是相同的),那么我将在其中创建多个对象,这些对象使用其调用的类的实例变量。因此,您可以了解为什么我调用super.methodIWantToReuse
时不起作用,因为它将获取父数据并将其传递到对象中,即使我 我真的希望它传递我在子类中初始化的数据。我的实际示例还在创建更多的对象,在实例中创建了更多的实例变量,因此我真的想尽可能地重用此代码(DRY原理)。
我该如何解决?将使用 getters 即getFirstName()
并将其覆盖到Child类中,因此在我调用super.methodIWantToReuse()
时使用运行时多态性将会 grab /使用 Child类实例变量数据是唯一的方法?
public class ParentClass {
private static final String firstName = "Billy Ray";
private static final String lastName = "Cyrus";
private static final int age = 58;
private static final String city = "Hunstville";
public boolean methodIWantToReuse() {
Object1 obj1 = new Object(firstName, lastName);
Object2 obj2 = new Object(age,city);
Object3 obj3 = new Object(obj1, obj2);
Object4 obj4 = new Object(obj3);
// Passing in the objects created above as argument, which have the Parent instance variable data
return someRandomMethodHere(obj4);
}
public class ChildClass {
private static final String firstName = "Miley";
private static final String lastName = "Cyrus";
private static final int age = 27;
private static final String city = "Los Angeles";
public boolean methodIWantToReuse() {
// DOESN'T WORK CORRECTLY, because ends up using the instance variable data of PARENT class, but it
// needs to use CHILD class instance variable data
super.methodIWantToReuse();
}
答案 0 :(得分:3)
您不能覆盖类的字段。只有方法可以被覆盖。在您的情况下,您必须使用getter并在子类中覆盖它们。
答案 1 :(得分:2)
您的父类实例变量对此是私有的,因此您不能从Child类更新它们。因此,您宁可使用parameterize方法或为实例变量(或受保护变量本身)创建Protected setter / getter。在您的情况下,变量是最终变量,因此实际上您甚至无法更新它们。因此从技术上讲,不可能在父类中使用子类变量。
如果将变量更新为protected
并删除static/final
修饰符(如您在注释中所提到的)。从父类调用方法之前,请在调用超级方法之前更新变量数据。您可以按照以下步骤进行操作:
方法1::在调用父类方法之前更新父类中的数据。
父级:
public class ParentClass {
protected String firstName = "Billy Ray";
protected String lastName = "Cyrus";
protected int age = 58;
protected String city = "Hunstville";
public boolean methodIWantToReuse() {
// Passing in the objects created above as argument, which have the Parent
// instance variable data
Object1 obj1 = new Object(firstName, lastName);
Object2 obj2 = new Object(age,city);
Object3 obj3 = new Object(obj1, obj2);
Object4 obj4 = new Object(obj3);
return someRandomMethodHere(obj4);;
}
}
儿童班:
public class ChildClass extends ParentClass {
protected String firstName = "Miley";
protected String lastName = "Cyrus";
protected int age = 27;
protected String city = "Los Angeles";
public boolean methodIWantToReuse() {
// Update data in Parent class first
super.firstName = firstName;
super.lastName = lastName;
super.age = age;
super.city = city;
return super.methodIWantToReuse();
}
}
方法2:如果要使用参数化方法使其变为无状态,则可以按以下步骤进行操作:
父级:
public class ParentClass {
protected String firstName = "Billy Ray";
protected String lastName = "Cyrus";
protected int age = 58;
protected String city = "Hunstville";
public boolean methodIWantToReuse() {
return methodIWantToReuse(this.firstName, this.lastName, this.age, this.city);
}
public boolean methodIWantToReuse(String firstName, String lastName, int age, String city) {
// Passing in the objects created above as argument, which have the Parent
// instance variable data
Object1 obj1 = new Object(firstName, lastName);
Object2 obj2 = new Object(age,city);
Object3 obj3 = new Object(obj1, obj2);
Object4 obj4 = new Object(obj3);
return someRandomMethodHere(obj4);;
}
}
儿童班:
public class ChildClass extends ParentClass {
protected String firstName = "Miley";
protected String lastName = "Cyrus";
protected int age = 27;
protected String city = "Los Angeles";
public boolean methodIWantToReuse() {
// Update data in Parent class first
return super.methodIWantToReuse(this.firstName, this.lastName, this.age, this.city);
}
}
注意:保持局部变量名称与类级别变量相同不是一种好习惯。但是为了理解起见,在这里保持相同。
答案 2 :(得分:0)
如果您的意思确实是instance variables
而不是示例中显示的static variables
(或class variables
),则可以通过更改access修饰符并删除来使它们可用于子类。 final
关键字。
但是,如果您实际上是指static variables
,则不能在每个子类中重新分配它们,因为它们都将共享由ParentClass
定义的相同静态变量,这意味着最后一个加载的类将是唯一的通过调用ParentClass#methodIWantToReuse
得到的结果。
最好是通过实例化带有所需参数的新单个对象并使用它们来利用OOP的优势。
这是我的意思,而不是这样做:
public class Example {
public static class ParentClass {
protected String name;
protected int age;
public ParentClass() {
name = "The parent";
age = 35;
}
public String methodIWantToReuse() {
return name + " is " + age + " years old.";
}
}
public static class AChildClass extends ParentClass {
public AChildClass() {
name = "Alice";
age = 13;
}
}
public static class AnotherChildClass extends ParentClass {
public AnotherChildClass() {
name = "Bob";
age = 21;
}
}
public static void main(String[] args) {
// Prints "The parent is 35 years old."
System.out.println(new ParentClass().methodIWantToReuse());
// Prints "Alice is 13 years old."
System.out.println(new AChildClass().methodIWantToReuse());
// Prints "Bob is 21 years old."
System.out.println(new AnotherChildClass().methodIWantToReuse());
}
}
执行此操作:
public class Example {
public static class ParentClass {
protected String name;
protected int age;
// Variables instantiated here to not cause confusion
public ParentClass() {
name = "The parent";
age = 35;
}
public String methodIWantToReuse() {
return name + " is " + age + " years old.";
}
}
public static class ChildClass extends ParentClass {
public ChildClass(String name, int age) {
this.name = name;
this.age = age;
}
}
public static void main(String[] args) {
// Prints "The parent is 35 years old."
System.out.println(new ParentClass().methodIWantToReuse());
// Prints "Alice is 13 years old."
System.out.println(new ChildClass("Alice", 13).methodIWantToReuse());
// Prints "Bob is 21 years old."
System.out.println(new ChildClass("Bob", 21).methodIWantToReuse());
}
}
这也应该遵循DRY原则,因为您想尽可能高效地重用代码,而不是一遍又一遍地进行技术上的重复编码。
如您所见,我不需要重写ParentClass#methodIWantToReuse
或调用ChildClass
的super的实现。