Java 派生类中的最终变量初始化

如果我们可以在基类的派生类中初始化基类的最后一个变量，我会感到困惑。 我的基础课是

    abstract class MyClass1 {
        //Compiler Error:Variable is not initialized in the default constructor.

        public final int finalVar;
    }
    //And my derived class with variable initialization.

    class DerivedClass extends MyClass1 {
        DerivedClass()
        {
            super();
            //Cannot asssign a value to finalVar.
            finalVar = 1000;
        }
   }

---

请告诉我是否可以初始化派生类中的最终变量。它只会产生编译时错误还是运行时错误？

您必须为父类中的变量赋值

// Declaring Parent class
class Parent {
    /* Creation of final variable pa of string type i.e 
    the value of this variable is fixed throughout all 
    the derived classes or not overidden*/
    final String pa = "Hello , We are in parent class variable";
}
// Declaring Child class by extending Parent class
class Child extends Parent {
    /* Creation of variable ch of string type i.e 
    the value of this variable is not fixed throughout all 
    the derived classes or overidden*/
    String ch = "Hello , We are in child class variable";
}

class Test {
    public static void main(String[] args) {
        // Creation of Parent class object
        Parent p = new Parent();
        // Calling a variable pa by parent object 
        System.out.println(p.pa);
        // Creation of Child class object
        Child c = new Child();

        // Calling a variable ch by Child object 
        System.out.println(c.ch);
        // Calling a variable pa by Child object 
        System.out.println(c.pa);
    }
}

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最终成员需要在类的构造函数中初始化。您可以修改代码，使子类通过构造函数传递值：

abstract class MyClass1 {

    public final int finalVar;

    protected MyClass1(int var) {
         finalVar = var;
    }

} 

class DerivedClass extends MyClass1 {
    DerivedClass() {
        super(1000);
    }
}

---

最后一个变量需要在构造函数中初始化，这是抽象类所缺少的。添加该构造函数之后，您可以通过super（）调用它。考虑下面的例子：

public class Main {
    public static void main(String[] args) {
        baseClass instance = new derivedClass(1);
    }
}

abstract class baseClass {
    protected final int finalVar;
    baseClass(int finalVar){
        this.finalVar = finalVar;
    }
}

class derivedClass extends baseClass {
    derivedClass(int finalVar){
        super(finalVar);
        System.out.println(this.finalVar);
    }
}

---

它只是给出编译时错误还是也会给出运行时错误。

-如果您的代码没有通过编译，您就无法运行它，因此该代码将没有运行时。您应该参考最终的变量声明文档！编译错误没有说明最终字段必须由基类构造函数初始化吗？为什么不运行它并自己找到答案？