类和对象练习

1.

public class Point {    int x;    int y;    double getDistance(){        double distance=Math.sqrt(x*x+y*y);        return distance;    }    public static  void main(String[] args){        Point p = new Point();        p.x=3;        p.y=4;        System.out.print(p.getDistance());    }}

2.

 public class FindWrong {    public static void main(String[] args) { int i=1, j; //j没有初始化        float f1 = 0.1, f2 = 123;  //0.1后面应该加f 或者 前面加(float)        final double PI = 3.1415926;        char class = 'b'//class 是关键字        i=j+5;        f1=f2+2;        PI=PI*2; //final不能改变        z ='c';    }}

3.

public class Point {    int x;    int y;    public Point(int x1,int y1){        x=x1;        y=y1;    }    double getDistance(){        double distance=Math.sqrt(x*x+y*y);        return distance;    }    public static  void main(String[] args){    Point p =new Point(3,4);    System.out.println(p.getDistance());    }}

4.

import java.awt.*;import java.sql.Statement;public class Line {    Point startPoint;    Point endPoint;    public Line(Point p1,Point p2){        startPoint = p1;        endPoint = p2;    }    public Line(int x1,int y1,int x2,int y2){       startPoint = new Point(x1,y1);       endPoint = new Point(x2,y2);    }    double getLength(){        int x = startPoint.x-endPoint.x;        int y = startPoint.y-endPoint.y;        double length=Math.sqrt(x*x+y*y);        return length;    }    public static void main(String[] args){        Point p1 = new Point(1,1);        Point p2 = new Point(2,2);        Line line1 = new Line(p1,p2);        System.out.print(line1.getLength());    }}

5.

public class Student {    int age;    String name;    static int count=0;    public  Student(){        System.out.println("调用无参的构造方法");        count++;    }    public Student(int age){this.age=age;        System.out.println("调用只有一个参数的构造方法");        this.age=age;    }    public  Student(int age,String name){this.age=age;this.name=name;        System.out.println("调用有两个参数的构造方法");    }    public void printlnfo(){        System.out.println(this.name+"的年龄是"+this.age);    }    public static void printCount(){        System.out.println("当前Count = : " + count);    }    public static void main(String[] ages){        Student s1 = new Student(20,"张三");        Student s2 = new Student(20,"张三");        s1.printlnfo();        s2.printlnfo();        //Student s3 = new Student(); 测试count        Student.printCount();    }}

6.

public class Account {    String account;    String name;    double balance;    double money;    double money1;    static double minBalance=10;   public  Account(String a,String n,double b)    {       account = a;       name = n;       balance =b;    }    public  void deposit(double money){        this.balance+=money;        System.out.println("原有金额为:"+(balance-money)+"现存金额为:"+money+"存入后的金额为:"+balance);    }    public void withdraw(double money1){        if((this.balance-money1)<minBalance)            System.out.println("提出金额失败！");        else            System.out.println("原有金额为:"+(balance)+"现存金额为:"+money1+"取出后的金额为:"+(balance-money1));    }    public static void setMinbalance(double minBalance) {        Account.minBalance = minBalance;    }    public  static  void main(String[] args){        Account people= new Account("77777","cxa",77777);        //存钱        people.deposit(33333);        //取钱        people.withdraw(33333);        //提出金额失败        people.withdraw(8888888);    }}