子类初始化的顺序
子类初始化时构造函数优于类中的字段
public class A {
private int mSuperX;
public A() {·
setX(99);
}
public static void main(String[] args) {
B sc = new B();
sc.printX();
}
public void setX(int x) {
mSuperX = x;
}
}
class B extends A {
private int mSubX = 1;
public B() {
}
@Override
public void setX(int x) {
super.setX(x);
mSubX = x;
System.out.println("SubX is assigned " + x);
}
public void printX() {
System.out.println("SubX = " + mSubX);
}
}输出结果为
SubX is assigned 99
1
构造子类B需要先是调用A的构造函数，由于setX被重写，然后执行了B中的setX方法输出99，然后初始化B中的字段mSubX = 1，完成B对象的初始化。
构造子类时会先调用父类的无参构造方法，即使调用的是子类的有参构造方法
public class A {
private int mSuperX;
public A() {
System.out.println("AAAAA");
}
public static void main(String[] args) {
C sc = new C(1);
}
public A (int x) {
System.out.println("A1");
}
}
class B extends A {
private int mSubX = 1;
public B() {
System.out.println("BBBBBBB");
}
public void printX() {
System.out.println("SubX = " + mSubX);
}
public B (int x) {
System.out.println("B1");
}
}
class C extends B{
public C(){
System.out.println("CCCCCC");
}
public C (int x) {
System.out.println("C1");
}
}输出结果为
AAAAA
BBBBBBB
C1