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When creating a derived class object, what is the execution order of constructors?
When creating a derived class object, what is the execution order of constructors?
Jul 08, 2020 pm 03:55 PM
When creating a derived class object, the execution order of the constructor is: base class constructor, derived class object member constructor, and the constructor of the derived class itself. When an object is created, the code loading order is: static code, non-static code, and constructor methods.
When creating a derived class object, the execution order of the constructor is: base class constructor, derived class object member constructor, and the constructor of the derived class itself.
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Detailed introduction:
The loading order of the code when the object is created is: static code --> Non-static code --> Constructor.
If the parent class is inherited, the loading order is: the static code of the parent class --> the static code of the subclass --> the non-static code within the parent class --> the parent class's Constructor --> Non-static code of the subclass --> Constructor of the subclass.
Among them, static code includes (static methods, static variables, static code blocks, etc.), non-static code is (member methods, member variables, member code blocks, etc.). The same type of code, written above load.
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Example:
public class ExtendsTest {
public static void main(String[] args) {
// TODO Auto-generated method stub
C c = new D();
}
}
class C {
static {
System.out.println("C 基類靜態(tài)域 ");
}
{
System.out.println("C 基類對(duì)象成員構(gòu)造函數(shù)");
}
public C() {
System.out.println("C 基類本身的構(gòu)造函數(shù)");
}
}
class D extends C {
static {
System.out.println("D 派生類靜態(tài)域");
}
{
System.out.println("D 派生類對(duì)象成員構(gòu)造函數(shù)");
}
public D() {
System.out.println("D 派生類本身的構(gòu)造函數(shù)");
}
}Output result:
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