1.throws
Throw an exception , Who calls who deals with
Declare an exception after a method Method name () throws Exception types
public class Test1_Exception {
public static void main(String[] args) {
// TODO Auto-generated method stub
// method();// Abnormal exposure
try {
method2();
} catch (ArithmeticException e) {
// TODO Auto-generated catch block
System.out.println(" The divisor is not 0");
}
}
public static void method2 () throws ArithmeticException{
int a=5;
int b=0;
System.out.println(a/b);
}
public static void method() {
// TODO Auto-generated method stub
int a=5;
int b=0;
System.out.println(a/b);
}
}2.abstract
By abstract The decorated method is called abstract method
Abstract methods can have no method bodies ;
There are abstract methods in a class , It's an abstract class
Abstract classes do not allow instantiation
Subclasses inherit Abstract parents , Or implement all the abstract methods of the parent class , Either it is defined as an abstract class
public class test2_Abstract {
public static void main(String[] args) {
// TODO Auto-generated method stub
Animal cat=new Cat();
cat.eat();
cat.sleep();
// Animal b=new Dog();// Abstract class cannot be instantiated
}
}
// When there are abstract methods in a class , So this class is an abstract class
abstract class Animal{
// Abstract methods can have no method bodies
public abstract void eat();
public void sleep() {
System.out.println(" Go to sleep ");
}
}
// When a class inherits an abstract class , Or rewrite the abstract method of the abstract class , Or it's also an abstract class
abstract class dog extends Animal{
}
class Cat extends Animal{
@Override
public void eat() {
// TODO Auto-generated method stub
System.out.println(" Cats eat fish ");
}
public void sleep() {
System.out.println(" Go to sleep +++++");
}
}
3.abstract Usage of
There can be construction methods in abstract classes , Abstract classes cannot be instantiated themselves , But its subclass instantiation , A parameterless construct of the parent class is required
ublic class Test3_UseAbstract {
public static void main(String[] args) {
// TODO Auto-generated method stub
Aniaml2 a=new dog2();
}
}
abstract class Aniaml2{
public Aniaml2() {
System.out.println(" The construction method of the parent class ");
}
}
class dog2 extends Aniaml2{
public dog2() {
super();
System.out.println(" Subclass construction method ");
// TODO Auto-generated constructor stub
}
}Variables and constants can exist in abstract classes , Subclass inherits abstract class , You can modify variables , You can't modify constants
public class Test4_UseAbstract2 {
public static void main(String[] args) {
// TODO Auto-generated method stub
Animal3 dog3=new Dog3();
dog3.name=" Poodle ";
System.out.println(dog3.name);
// dog3.MAX_VLAUE=18;
System.out.println(dog3.MAX_VLAUE);
}
}
abstract class Animal3{
String name=" rhubarb ";
public static final byte MAX_VLAUE=127;
}
class Dog3 extends Animal3{
} Abstract classes can all be ordinary methods , Abstract classes cannot be instantiated
Abstract classes can have ordinary methods and abstract methods
Subclass inherits abstract class , Or rewrite all the abstract methods of the abstract class , Or defined as an abstract class . When a child class does not override the normal method of the parent class, it accesses the normal method of the parent class , After being overridden, the subclass's rewriting method is accessed .
public class Test5_UseAbstract3 {
public static void main(String[] args) {
// TODO Auto-generated method stub
Animal4 a=new Dog4();
a.sleep();// Common method -- Using the parent class before rewriting , After rewriting, subclasses are used
a.eat();// Abstract method -- Using the method of the parent class to declare , Method body of subclass
a.game();// Abstract method -- Using the method of the parent class to declare , Method body of subclass
}
}
abstract class Animal4{
public void sleep() {
System.out.println("sleep()...");
}
public abstract void eat();
public abstract void game();
}
class Dog4 extends Animal4{
@Override
public void eat() {
// TODO Auto-generated method stub
System.out.println("eat()...");
}
@Override
public void game() {
// TODO Auto-generated method stub
System.out.println("game()...");
}
}
abstract class Cat4 extends Animal4{
@Override
public void eat() {
// TODO Auto-generated method stub
System.out.println("eat222()...");
}
}abstact example
-- demand :
Concrete things : Teacher of Peiyou class , Master class teacher
Generality : Prepare lessons / lecture
test : Creating polymorphic object tests
public class Test6_Design {
public static void main(String[] args) {
// TODO Auto-generated method stub
Teacher cGBTeacher=new CGBTeacher();
Teacher actTeacher=new ActTeacher();
cGBTeacher.ready();
cGBTeacher.teach();
actTeacher.ready();
actTeacher.teach();
}
}
abstract class Teacher{
public abstract void ready();
public abstract void teach();
}
class CGBTeacher extends Teacher{
@Override
public void ready() {
// TODO Auto-generated method stub
System.out.println(" Teacher of Peiyou class Get ready E-commerce projects ");
}
@Override
public void teach() {
// TODO Auto-generated method stub
System.out.println(" Teacher of Peiyou class speak E-commerce projects ");
}
}
class ActTeacher extends Teacher{
@Override
public void ready() {
// TODO Auto-generated method stub
System.out.println(" Master class teacher Prepare the handwriting frame ");
}
@Override
public void teach() {
// TODO Auto-generated method stub
System.out.println(" Master class teacher Talk about the strengthening part ");
}
}
