本人是大二学生,学识尚浅,想知道为什么这串代码会报错
java8版本
package test;
import java.lang.reflect.Constructor;
import java.util.Objects;
class A {
int num;
A(){
System.out.println("A() is running");
}
A(int num) {
this.num = num;
System.out.println("A(int) is running");
System.out.println("num: " + num);
}
public int getNum() {
return num;
}
public void setNum(int num) {
this.num = num;
}
@Override
public boolean equals(Object o) {
if (this == o) return true;
if (o == null || getClass() != o.getClass()) return false;
A a = (A) o;
return num == a.num;
}
@Override
public int hashCode() {
return Objects.hash(num);
}
}
public class Test03 {
public static void main(String[] args) throws Exception {
A a = new A();
Class cl = a.getClass();
fun(a);
}
static Object fun(Object o) throws Exception {
Class<?> aClass = o.getClass();
System.out.println(aClass);
Constructor<?> constructors = aClass.getConstructor();
Object o1 = constructors.newInstance();
return o;
}
}
报错内容为
A() is running
class test.A
Exception in thread "main" java.lang.NoSuchMethodException: test.A.<init>()
at java.lang.Class.getConstructor0(Class.java:3082)
at java.lang.Class.getConstructor(Class.java:1825)
at test.Test03.fun(Test03.java:51)
at test.Test03.main(Test03.java:45)
Process finished with exit code 1
网上查了一些用反射调用构造器的例子,他们似乎都不会出现问题。
如果反射Random.class则不会出现问题,将构造器权限改为public也不会出现问题,但是其他人的例子是默认访问权限的。