看代码说结果

public class Dervied extends Base {
private String name = "dervied";
public Dervied() {
tellName();
printName();
}
public void tellName() {
System.out.println("Dervied tell name: " + name);
}
public void printName() {
System.out.println("Dervied print name: " + name);
}
public static void main(String[] args){
new Dervied();
}
}
class Base {
private String name = "base";
public Base() {
tellName();
printName();
}
public void tellName() {
System.out.println("Base tell name: " + name);
}
public void printName() {
System.out.println("Base print name: " + name);
}
}

运行结果:
Dervied tell name: null
Dervied print name: null
Dervied tell name: dervied
Dervied print name: dervied

为什么会这样呢
并且无论修改Base的name为public还是protected,结果都是这样.
甚至代码改成这样,还是这个结果(Base类的name字段改成了basename)

public class Dervied extends Base {
private String name = "dervied";
public Dervied() {
tellName();
printName();
}
public void tellName() {
System.out.println("Dervied tell name: " + name);
}
public void printName() {
System.out.println("Dervied print name: " + name);
}
public static void main(String[] args){
new Dervied();
}
}
class Base {
public String basename = "base";
public Base() {
tellName();
printName();
}
public void tellName() {
System.out.println("Base tell name: " + basename);
}
public void printName() {
System.out.println("Base print name: " + basename);
}
}

后台一个大神一语道破
Base的构造函数中,调用的两个方法tellName和printName,因为继承的原因,应该执行的是子类的方法,而子类此时还没有初始化这个数据成员,所以显示为null.

ITPub博客

JAVA继承的初始化问题

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