Java构造函数的调用顺序的详细介绍
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:
classCake{
Cake(){System.out.println("Cake()");}
}
classMeal{
Meal(){System.out.println("Meal()");}
}
classBread{
Bread(){System.out.println("Bread()");}
}
classCheese{
Cheese(){System.out.println("Cheese()");}
}
classLettuce{
Lettuce(){System.out.println("Lettuce()");}
}
classLunchextendsMeal{
Lunch(){System.out.println("Lunch()");}
}
classPortableLunchextendsLunch{
//ifmakederived-classobjectasthemenberofthebase-classwillleadainfinite
//loopandprogramwillstopbecauseofthememoryconsumed
//privateSandwichs=newSandwich();
privateCakea=newCake();
PortableLunch(){System.out.println("PortableLunch()");}
}
publicclassSandwichextendsPortableLunch
{
privateBreadb=newBread();
privateCheesec=newCheese();
privateLettucel=newLettuce();
publicSandwich(){
System.out.println("Sandwich()");
}
publicstaticvoidmain(String[]args){
newSandwich();
}
}
Cake(){System.out.println("Cake()");}
}
classMeal{
Meal(){System.out.println("Meal()");}
}
classBread{
Bread(){System.out.println("Bread()");}
}
classCheese{
Cheese(){System.out.println("Cheese()");}
}
classLettuce{
Lettuce(){System.out.println("Lettuce()");}
}
classLunchextendsMeal{
Lunch(){System.out.println("Lunch()");}
}
classPortableLunchextendsLunch{
//ifmakederived-classobjectasthemenberofthebase-classwillleadainfinite
//loopandprogramwillstopbecauseofthememoryconsumed
//privateSandwichs=newSandwich();
privateCakea=newCake();
PortableLunch(){System.out.println("PortableLunch()");}
}
publicclassSandwichextendsPortableLunch
{
privateBreadb=newBread();
privateCheesec=newCheese();
privateLettucel=newLettuce();
publicSandwich(){
System.out.println("Sandwich()");
}
publicstaticvoidmain(String[]args){
newSandwich();
}
}
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