Previously, the polymorphism has always been very vague, today is free, I have a special test.
Bean classes to operate on
//Non-static variables
class A{
int a = 1;
}
class B extends A{
int a = 3;
int b = 2;
}
//Static variables
class AA{
static int a = 1;
}
class BB extends AA{
static int a = 2;
}
class CC extends AA{
static int a = 3;
}
class M1{
static void show(){
System.out.println("M1.show()");
}
}
class M2 extends M1{
static void show(){
System.out.println("M2.show()");
}
}
public class Bean {
}
***********************************************************************************************************************************************
Test class
import org.junit.Test;
public class Test1 {
//Non-static variables can be inherited (int a)
@Test
public void test1(){
A a = new A();
System.out.println(a.a);//1
B b = new B();
System.out.println(b.a);//1
System.out.println(b.b);//2
}
//Non-static variables are determined at compile time and cannot be overridden. In fact, rewriting is about methods.
@Test
public void test2(){
B b = new B();
System.out.println(b.a);//3
System.out.println(b.b);//2
A ab = new B();
System.out.println(ab.a);//1
//b cannot be resolved or is not a field
//System.out.println(ab.b);//1
}
//Static variables can be inherited
@Test
public void test3(){
AA aa = new AA();
System.out.println(aa.a);//1
System.out.println(AA.a);//1
//Variables with the same name of different types are not declared in BB
BB bb = new BB();
/*System.out.println(bb.a);//1
System.out.println(BB.a);//1
*/
//If a non-static variable int a = 2 with the same name is declared to subclass BB;
/*System.out.println(bb.a);//2
System.out.println(BB.a);//Compile and report errors
*/
//If a static variable statiint a = 2 with the same name is declared to subclass BB;
System.out.println(bb.a);//2
System.out.println(BB.a);//2
}
//Static variables cannot be overridden either
@Test
public void test4(){
AA ac = new CC();
//Variables with the same name of different types are not declared in CC
//System.out.println(ac.a);//1
//If a non-static variable int a = 2 with the same name is declared to subclass CC;
System.out.println(ac.a);//1
//If a static variable statiint a = 2 with the same name is declared to subclass BB;
System.out.println(ac.a);//1
}
//Static methods can be inherited
@Test
public void test5(){
M2 m2 = new M2();
m2.show();//M1.show()
M2.show();//M1.show()
}
//Static methods cannot be overridden
@Test
public void test6(){
M1.show();//M1.show()
M2.show();//M2.show()
//If a static void show() method with the same name and parameter is declared in subclass M2, then the static method of the parent class is hidden.
M2 m2 = new M2();
m2.show();//M2.show()
//Upward transition (polymorphism) parent static methods are not rewritten
M1 m12 = new M2();
m12.show();//M1.show(), indicating that the parent static method was not overridden
}
}