java中构造函数的调用顺序
当一个复杂的对象被构造时,它的构造函数按下面的顺序被调用(that the order of constructor calls for a complex object is as follows)
1.其基类(base-class)的构造函数被调用,这个步骤以递归的方式重复,所以最底层(the root of hierarchy)的构造函数首先被执行,然后是它上一层派生类(the next-derived class)...直到最顶层的派生类(the most-derived class).
The base-class constructor is called. This step is repeated recursively such that the root of the hierarchy is constructed first, followed by the next-derived class, etc., until the most-derived class is reached.)
2.如果有包含关系(composition),那么它的成员对象按照声明的顺序被构造.
Member initializers are called in the order of declaration.
3.派生类构造函数的内容(body)被执行.
The body of the derived-class constructor is called.
一个实例:
class Cake{
Cake(){System.out.println("Cake()");}
}
class Meal {
Meal() { System.out.println("Meal()"); }
}
class Bread {
Bread() { System.out.println("Bread()"); }
}
class Cheese {
Cheese() { System.out.println("Cheese()"); }
}
class Lettuce {
Lettuce() { System.out.println("Lettuce()"); }
}
class Lunch extends Meal {
Lunch() { System.out.println("Lunch()"); }
}
class PortableLunch extends Lunch {
//if make derived-class object as the menber of the base-class will lead a infinite
//loop and program will stop because of the memory consumed
//private Sandwich s=new Sandwich();
private Cake a=new Cake();
PortableLunch() {&n
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