本文共 4618 字，大约阅读时间需要 15 分钟。
import java.util.*;
public class Main{
public static void main(String[] args){
Scanner scanner=new Scanner(System.in);
int year=scanner.nextInt();
if(year%100==0){
if(year%400==0){
System.out.println(year+"是闰年");
}else
System.out.println(year+"不是闰年");
}else if(year%4==0){
System.out.println(year+"是闰年");
}else
System.out.println(year+"不是闰年");
}
}//闰年
import java.util.*;
public class Main{
public static void main(String[] args){
for(int i=1;i<10;i++){
for(int j=1;j<=i;j++){
System.out.print(i+"*"+j+"="+i*j);
System.out.print(" ");
}
System.out.println();
}
}
}//九九乘法
第三章 类和多态
import java.util.Scanner;
public class Rectangle{
private double length;
private double width;
private double permeter;
private double area;
public Rectangle(){
}
public Rectangle(double length,double width){
this.length=length;
this.width=width;
}
double getlength(){
return length;
}
void setlength(double length){
this.length=length;
}
double getwidth(){
return width;
}
void setwidth(double width){
this.width=width;
}
public double permeter(){
return 2*(length+width);
}
public double area(){
return length*width;
}
void print(){
System.out.println("长方形的长为："+length);
System.out.println("长方形的宽为："+width);
System.out.println("长方形的周长为："+permeter());
System.out.println("长方形的面积为："+area());
}
public static void main(String []args){
Scanner input =new Scanner(System.in);
System.out.println("请输入长方形的长：");
double length=input.nextDouble();
System.out.println("请输入长方形的宽");
double width=input.nextDouble();
//利用构造方法
Rectangle rectangle=new Rectangle(length,width);
rectangle.print();
}
}
/*请输入长方形的长：
8
请输入长方形的宽
3
长方形的长为：8.0
长方形的宽为：3.0
长方形的周长为：22.0
长方形的面积为：24.0*/
第四章 类间关系
//1.多态函数重写
public class base{
public void print(){
System.out.println("in base");
}
public static void main(String[] args){
son obj=new son();
obj.print();
}
}
class son extends base{
public void print(){
System.out.println("in son");
}
}//in son
//2.继承 多态
public class base{
public void print(){
System.out.println("in base");
}
static void test(base base){
base.print();
}
public static void main(String[] args){
son obj=new son();
test(new base());
test(new son());
test(new son1());
}
}
class son extends base{
public void print(){
System.out.println("in son");
}
}
class son1 extends base{
public void print(){
System.out.println("in son1");
}
}//in base
//in son
//in son1
多态 super调用父类构造方法，父类属性和方法
不用getset
public class Main{
private String name;
private int age;
private String sex;
public Main(){
System.out.println("无参构造函数");
}
public Main(String name,int age,String sex){
System.out.println("有参构造函数");
this.name = name;
this.age = age;
this.sex = sex;
}
public void print(){
System.out.println("name:"+name);
System.out.println("age:"+age);
System.out.println("sex:"+sex);
}
public static void main(String []args){
teacher zhang=new teacher("zhang",50,"nan",800000);
zhang.print();
}
}
class teacher extends Main{
private float salary;
public teacher(){
}
public teacher(String name,int age,String sex,float salary){
super(name,age,sex);
this.salary = salary;
}
public void print(){
super.print();
System.out.println("salary:"+salary);
}
}
/*有参构造函数
name:zhang
age:50
sex:nan
salary:800000.0*/
/*有参构造函数
name:zhang
age:50
sex:nan
salary:800000.0*/
/*有参构造函数
name:zhang
age:50
sex:nan
salary:800000.0*/
/*有参构造函数
name:zhang
age:50
sex:nan
salary:800000.0*/
第五章 抽象类、接口和内部类
抽象类的继承
public abstract class Shape{
double dim;
public Shape (double dim){
this.dim=dim;
}
public abstract double CallPerimeter();
public abstract double CallArea();
}
//public类只能出现在一个文件中
public class Circle extends Shape{
public Circle(double dim){
super(dim);
}
public double CallPerimeter(){
return 2*3.14*dim;
}
public double CallArea(){
return 3.14*dim*dim;
}
public static void main(String []args){
Shape shape=new Circle(10);
System.out.println("圆的周长"+shape.CallPerimeter());
System.out.println("圆的面积"+shape.CallArea());//实现所有方法
}
}
接口定义 、实现、Instanceof运算符、对象强制类型转化（object所有子类的顶级父类 到具体类）
interface Ibase{
public void print();
}
class Base implements Ibase{
int b;
Base(int b){
this.b=b;
}
public void print(){
System.out.println("in Base!");
}
}
class Base1 extends Base{
int c;
public Base1(int b,int c){
super(b);
this.c=c;
}
public void print(){
System.out.println("in Base1!");
}
}
public class Main{
public static void typeof(Object obj){
if(obj instanceof Base){
Base base=(Base)obj;
base.print();
}else if(obj instanceof Base1){
Base1 base1=(Base1)obj;
base1.print();
}
}
public static void main(String []args){
Base b1=new Base(1);
Base1 b2=new Base1(2,3);
System.out.print("b1 is ");
typeof(b1);
System.out.print("b2 is ");
typeof(b2);
}
}
/*
b1 is in Base!
b2 is in Base1!
*/
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