Experiment five categories and objects

Experiment five    Classes and objects

The experiment purpose

1. master Java Definition of language category 、 Object creation 、 Object reference method .

2. Have a preliminary understanding of object-oriented design methods

Experimental hours 6 Class hours

Experimental content

1. Design a ballpoint pen class BallPen, Yes 1 Attributes boolean penPoint（ Whether the nib extends ）, Yes 4 A way ：

   （1） Construction method BallPen (), take penPoint Set as false

   （2） Press operation method void  knock(), take penPoint Inversion

   （3） How to get the nib state boollean getPenPoint()

   （4）main Method

     Create an object and press the instance object , Display the status of the nib .

package code51;

public class BallPen {  // take penPoint Set as false

boolean penPoint;

BallPen() {

penPoint=false;

}

void knock() {  // take penPoint Inversion

if(penPoint==false)

{

penPoint=true;

}

else

{

penPoint=false;

}

}

boolean getPenPoint() {  // Get the nib status

return penPoint;

}

public static void main(String args[]) {

BallPen a = new BallPen();  // Create objects

a.knock();  // Press the instance object

System.out.println("penPoint="+a.getPenPoint());  // Display the status of the nib

}

}

2. Design a car class Car, Yes 2 Attribute owner owner And oil quantity oil, Yes 7 A way ：

（1） Construction method Car(String owner,double oil)

   （2） Construction method Car(String owner), Set the oil volume to 0

   （3） Refueling operation method void  addOil(double oil)

   （4） Driving operation method void  drive(int distance)

         Suppose that every 100 The fuel consumption per kilometer is a constant （ Set up your own ）, Update the fuel volume according to the mileage .

   （5） How to get owner information String  getOwner()

   （6） Method of obtaining oil quantity double getOil()

   （7）main Method

         Create an object and refuel the instance object 、 Driving operation , Show owner 、 Oil quantity .

package code52;

public class Car {

    String owner;

    double oil;

double x;

int distance;

Car(String owner,double oil) {

this.owner=owner;

this.oil=oil;

}

Car(String owner) {  // Set the oil volume to 0

oil=0;

}

void addOil(double oil) {  // Refuel

oil+=x;

}

void drive(int distance) {  // Update the fuel volume according to the mileage

oil-=(distance/100*10);

}

String getOwner() {  // Get owner information

return owner;

}

double getOil() {  // Get the oil quantity

return oil;

}

public static void main(String args[]) {

Car a = new Car(" Bowen huang ",100);  // Create objects

a.addOil(100);  // Refuel the instance object

a.drive(200);  // Run the instance object

System.out.println("owner="+a.getOwner());  // Show owner

System.out.println("oil="+a.getOil());  // Display the oil quantity

}

}

3. Write a class to represent coordinate points , Class contains constructor to assign coordinates when creating a new class . Write another tool class about coordinate points .

（1） Write coordinate point class Point.

   （2） Write a tool class PointUtil, Contains methods double distance(Point a,Point b) Used to calculate the distance between two coordinate points , And methods double area(Point a,Point b) It is used to calculate the rectangular area where the line between two points is diagonal .

   （3） Write the main method to calculate the coordinates （2,10） To coordinates （4,55） Distance between and rectangular area .

package code53;

public class PointUtil {

int x;

int y;

public PointUtil(int x,int y) {

this.x=x;

this.y=y;

}

double distance(PointUtil x1,PointUtil x2)

{

    double distance=Math.sqrt((x1.x-x2.x)*(x1.x-x2.x)+(x1.y-x2.y)*(x1.y-x2.y));

return distance;  // Find the distance between two coordinate points

}

double area(PointUtil x1,PointUtil x2)

{

double area=(x1.x-x2.x)*(x1.y-x2.y);

if(area<0)

{

area=-area;

}

return area;  // Find the area of a rectangle with two diagonal lines

}

}

package code53;

import java.util.Scanner;

public class Point {

public static void main(String args[]) {

Scanner in = new Scanner(System.in);

System.out.println(" Please enter the coordinates of the two points :");

PointUtil x1 = new PointUtil(in.nextInt(),in.nextInt());  // Create objects and point x1 Coordinate assignment

PointUtil x2 = new PointUtil(in.nextInt(),in.nextInt());  // Create objects and point x2 Coordinate assignment

double distance=x1.distance(x1, x2);  // Call the method to find the distance between two points

double area=x1.area(x1, x2);  // Call method to calculate rectangular area

System.out.println(" The distance between the two coordinate points is :"+distance);

System.out.println(" The area enclosed in a rectangle is :"+area);

}

}

4. To write Java The program simulates a simple calculator . Definition is named Number Class , There are two private integer data members x and y. Yes 7 A way ：

（1） Construction method Number(int x,int y)

（2） Addition method int addition(int x,int y)

（3） Subtraction method int subtration(int x,int y)

（4） Multiplication method int multiplication(int x,int y)

（5） Division operation method int division(int x,int y)

Write another test class , Yes Number Class to test .

package code54;

public class Number {

 int x,y;

 Number(int x,int y) {

 this.x = x;

 this.y = y;

 }

 int addition(int x,int y) {  // To add

 return x+y;

 }

 int subtration(int x,int y) {  // Do subtraction

 return x-y;

 }

 int multiplication(int x,int y) {  // Multiply

 return x*y;

 }

 int division(int x,int y) {  // Do Division

 return x/y;

 }

}

package code54;

import java.util.Scanner;

public class TextNumber {

public static void main(String args[]) {

 Scanner in = new Scanner(System.in);

 int x = in.nextInt();

 int y = in.nextInt();

 Number a = new Number(x,y);  // Create objects

 System.out.println("x+y="+a.addition(x, y));  // Call the addition method

 System.out.println("x-y="+a.subtration(x, y));  // Call the subtraction method

 System.out.println("x*y="+a.multiplication(x, y));  // Call the multiplication method

 System.out.println("x/y="+a.division(x, y));  // Call the division method

 }

}

5. Define a rectangle class Rectangle, contain ：

（1） attribute

int width;

int height;

    （2） Method

        Rectangle()： wide 、 High the default value is 1;

   Rectangle(int val): wide 、 All heights are parameter values ;

Rectangle(int width,int height)：

Double getSquare()： Calculated area ;

Double getPerimeter(): Circumference calculation ;

In addition, write test classes to test .

package code55;

public class Rectangle {

int width;

int height;

Rectangle()  // wide 、 High the default value is 1

{

width=1;

height=1;

}

Rectangle(int val)  // wide 、 All heights are parameter values

{

width=val;

height=val;

}

Rectangle(int width,int height) {

this.width=width;

this.height=height;

}

Double getSquare()  // Calculated area

{

double square;

square=width*height;

return square;

}

Double getPerimeter()  // Circumference calculation

{

double c;

c=width*2+height*2;

return c;

}

}

package code55;

import java.util.Scanner;

public class TextRectangle {

public static void main(String[] args) {

Scanner in = new Scanner(System.in);

System.out.println(" Please enter the width and height of the rectangle :");

int width=in.nextInt();

int height=in.nextInt();

Rectangle a=new Rectangle(width, height);  // Create objects

System.out.println(" Area is "+a.getSquare()+","+" The perimeter of "+a.getPerimeter());  // Call the method to find the area and perimeter

}

}

6. Define a time class MyTime, There are three properties hour,minute,second. by MyTime Construct method definitions , To initialize member variables when creating objects . In addition to the construction method , Also create the following methods ：

（1）nextSecond( )： Time passed 1 second

（2）nextMinute( )： Time passed 1 branch

（3）nextHour( )： Time passed 1 Hours

（4）prevSecond( )： front 1 second

（5）prevMinute( )： front 1 branch

（6）prevHour( )： The last hour

（7）display( )： With HH:MM:SS Format display time

In addition, write test classes , To test .

package code56;

public class MyTime {

int hour;

int minute;

int second;

public MyTime(int hour, int minute, int second) {

this.hour=hour;

this.minute=minute;

this.second=second;

}

void nextSecond()  // After a second

{

if(second!=59) second+=1;

else

{

second=0;

if(minute!=59) minute+=1;

else

{

minute=0;

if(hour!=23) hour+=1;

else

{

hour=0;

}

}

}

}

void nextMinute()  // After a minute

{

if(minute!=59) minute+=1;

else

{

minute=0;

if(hour!=23) hour+=1;

else

{

hour=0;

}

}

}

void nextHour()  // After an hour

{

if(hour!=23) hour+=1;

else

{

hour=0;

}

}

void prevSecond() {  // The second before

if(second!=0) second-=1;

else

{

second=59;

if(minute!=0) minute-=1;

else

{

minute=59;

if(hour!=0) hour-=1;

else

{

hour=23;

}

}

}

}

void prevMinute() {  // Previous point

if(minute!=0) minute-=1;

else

{

minute=59;

if(hour!=0) hour-=1;

else

{

hour=23;

}

}

}

void prevHour()  // The last hour

{

if(hour!=0) hour-=1;

else

{

hour=23;

}

}

void display()  // Press HH：MM：SS Time is displayed in the format of

{

System.out.println(hour+":"+minute+":"+second);

}

}

package code56;

import java.util.Scanner;

public class TextMyTime {

public static void main(String[] args) {

int hour=0,minute=0,second=0;

MyTime a=new MyTime(hour,minute,second);  // Create an object and assign a value

Scanner in = new Scanner(System.in);

a.hour=in.nextInt();

a.minute=in.nextInt();

a.second=in.nextInt();

a.prevHour();  

a.nextMinute();

a.nextSecond();  // Call methods to test

a.display();  // Display the time in the specified format

}

}

7. Write programs using plural classes Complex Verify two complex numbers  2+2i  and 3+3i  Add to produce a new complex number 5+5i . Plural Complex Meet the following requirements ：

（1） attribute

int realPart ： The real part of a complex number ;

int imaginPart： The imaginary part of the plural ;

（2） Method

Complex( ) :  Construction method , Set both the real and imaginary parts of a complex number to 0;

Complex( int r , int i ) : 

Complex complexAdd(Complex a) :  Add the current complex object to the formal parameter complex object , The result The result is still a complex value , Return to the caller of this method .

String toString( ) :  The real part of the current complex object 、 The imaginary parts are combined into  a+bi  String form of , among a  and  b Data of real part and imaginary part respectively .

Write another test class Test, Yes Complex Class to test .

package code57;

public class Complex {

int realPart;

int imaginPart;

Complex() {

realPart=0;

imaginPart=0;  // Set both the real and imaginary parts of the complex number to 0

}

Complex(int r,int i) {

realPart=r;

imaginPart=i;

}

Complex complexAdd(Complex a)

{

realPart+=a.realPart;

imaginPart+=a.realPart;  // Add the current complex object to the formal parameter complex object

return a;

}

public String toString()  // Combine the real and imaginary parts of the current complex object into a+bi String form of

{

return realPart+"+"+imaginPart+"i";

}

}

package code57;

public class TestComplex {

public static void main(String args[]) {

Complex a=new Complex(1,1);  

Complex b=new Complex(2,2);  // Create an object and assign a value

a.complexAdd(b);  // The calling method will a、b Add the two parts of

System.out.println(a.toString());  // Output its combination form

}

}

Summary of experiments

1. class ： Is a collection of abstract concepts , It represents a common product , Class defines properties and behaviors （ Method ）;
2. object ： Object is a representation of personality , Represents an independent individual , Each object has its own independent properties , Rely on attributes to distinguish different objects ;
3. stay Java Class , Use keywords class complete ;
4. object . attribute ： Represents the property in the calling class ;
5. object . Method （）： Means to call a method in a class ;
6. If a constructor has been clearly defined in a class , Then the parameterless constructor will not be automatically generated ;
7. this Keywords can be used to call properties of this class 、 Method 、 object .