Java是面向对象的编程语言。继承是最重要的功能之一。
我们使用封装来隐藏对象状态。在下面的程序中，我应该使用private访问修饰符来设置年龄和计数器，但是为了测试这种继承，我应该使用public。
为什么在直接对象状态访问的情况下继承不起作用
（原始类型或对象引用）。 SOP 3的输出与预期的不同。
由于编译器在SOP 13和SOP 14行中未给出任何错误，因此为什么显示父亲类详细信息而不是子类。
。
public class Father {
public int age = 50;
/*
* Counter keeps track of total no of instances created so far.
*/
public static int counter = 0;
public Father(){
super();
synchronized (Father.class) {
++Father.counter;
}
}
public int getAge(){
return this.age;
}
public static int getStaticCount(){
return Father.counter;
}
}
public class Child extends Father {
public int age = 25;
public static int counter = 0;
public Child(){
super();
synchronized (Child.class) {
++Child.counter;
}
}
public int getAge(){
return this.age;
}
public static int getStaticCount(){
return Child.counter;
}
public static void main(String args[]){
Father father = new Father();
Father child = new Child();
Child realChild = new Child();
System.out.println("Expecting Father Class details to be printed");
System.out.println("SOP 1 : Father Age : "+father.age); //prints 50 as expected.
System.out.println("SOP 2 : Father Age : "+father.getAge());//prints 50 as expected.
System.out.println("Expecting Child Class details to be printed");
/*
* Why inheritance does not work in case of direct integer access.
*/
System.out.println("SOP 3 : Child Age : "+child.age); //prints 50 ?? , Father Age . Why ?
System.out.println("SOP 4 : Child Age : "+child.getAge());//prints 25 as expected.
System.out.println("Expecting Child Class details to be printed");
System.out.println("SOP 5 : Child Age : "+realChild.age); //prints 25 as expected.
System.out.println("SOP 6 : Child Age : "+realChild.getAge());//prints 25 as expected.
/*
*Total No of static Count : proper way of accessing static field using Class Name.
*/
System.out.println("SOP 7 : Father Instance Count : Using Class Reference :"+Father.counter);
System.out.println("SOP 8 : Father Instance Count : Using Class Reference :"+Father.getStaticCount());
/*
* Incorrect Way to use static. Since Compiler allows this lets see output.
*/
System.out.println("SOP 9 : Father Instance Count : Using Object Reference :"+father.counter); //prints 3 as expected.
System.out.println("SOP 10 : Father Instance Count : Using Object Reference :"+father.getStaticCount());//prints 3 as expected.
/*
*Total No of static Count : proper way of accessing static field using Class Name.
*/
System.out.println("SOP 11 : Child Instance Count : Using Class Reference :"+Child.counter); // output is 2 as expected
System.out.println("SOP 12 : Child Instance Count : Using Class Reference :"+Child.getStaticCount()); // output is 2 as expected
/*
* Incorrect Way to use static.Since Compiler allows this lets see output.
* This invokes function of parent class. Why ? Inheritance does not work for static fields.
*/
System.out.println("SOP 13 : child Instance Count : Using Object Reference :"+child.counter); // output is 3 but expected is 2 . why ?
System.out.println("SOP 14 : child Instance Count : Using Object Reference :"+child.getStaticCount()); // output is 3 but expected is 2 . why ?
/*
* Incorrect Way to use static.Since Compiler allows this lets see output.
* This invokes function of parent class. Why ?
*/
System.out.println("SOP 15 : child Instance Count : Using Object Reference :"+realChild.counter); // output is 2 as expected
System.out.println("SOP 16 : child Instance Count : Using Object Reference :"+realChild.getStaticCount()); // output is 2 as expected
}
}
我的问题是为什么继承仅适用于实例方法。为什么SOP 3，SOP 13和SOP 14的输出不同
最佳答案
原因是多态性不适用于实例变量。您正在做的是可变阴影。
在SOP 3和4中，子类中具有相同名称的变量在基类中隐藏该变量。并且由于这是在编译时解决的，因此选择了静态类型的值。
在SOP 13和SOP 14中，发生这种情况的原因相同。在该方法的范围内，孩子的类隐藏变量是未知的。
从JSL：
在一个成员中声明或继承的成员m的声明范围
类类型C（第8.1.6节）是C的整个主体，包括任何嵌套的
类型声明。
关于java - Java中的继承:对象状态和行为，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/12440348/