J2SE之面向对象_重载_this_static_package_import_继承_访问控制

方法的重载

构造方法重载

对象的创建和使用

class Point {
    private double x;
    private double y;
    Point(double x1, double y1) {
        x = x1;
        y = y1;
    }
    public double getX() { return x; }
    public double getY() { return y; }
    public void setX(double i) { x = i; }
    public void setY(double i) { y = i; }
}

class Circle {
    private Point o;
    private double radius;
    Circle(Point p, double r) {
        o = p;
        radius = r;
    }
    Circle(double r) {
        o = new Point(0.0, 0.0);
        radius = r;
    }

    boolean contains(Point p) {
        double x = p.getX() - o.getX();
        double y = p.getY() - o.getY();
        if(x*x + y*y > radius * radius) return false;
        else return true;
    }

    public void setO(double x, double y) {
        o.setX(x);
        o.setY(y);
    }
    public Point getO() { return o; }
    public double getRadius() { return radius;}
    public void setRadius(double r) { radius = r;}
    public double area() {
        return 3.14 * radius * radius;
    }
}

public class TestCircle {
    public static void main(String args[]) {
        Circle c1 = new Circle(new Point(1.0,2.0), 2.0);
        Circle c2 = new Circle(5.0);
        System.out.println("c1:("+c1.getO().getX()+","
            +c1.getO().getY()+"),"+c1.getRadius());
        System.out.println("c2:("+c2.getO().getX()
            +","+c2.getO().getY()+"),"+c2.getRadius());
        System.out.println("c1 area = "+c1.area());
        System.out.println("c1 area = "+c2.area());
        c1.setO(5,6);
        c2.setRadius(9.0);
        System.out.println("c1:("+c1.getO().getX()+","
            +c1.getO().getY()+"),"+c1.getRadius());
        System.out.println("c2:("+c2.getO().getX()+","
            +c2.getO().getY()+"),"+c2.getRadius());
        System.out.println("c1 area = "+c1.area());
        System.out.println("c1 area = "+c2.area());

        Point p1 = new Point(5.2, 6.3);
        System.out.println(c1.contains(p1));
        System.out.println(c1.contains(new Point(10.0,9.0)));

    }
}

TestCircle.java

this关键字

static关键字

public class Cat {
    private static int sid = 0;
    private String name;
    int id;
    Cat(String name) {
        this.name = name;
        id = sid++;
    }
    public void info(){
        System.out.println
               ("My name is "+name+" No."+id);
    }
    public static void main(String arg[]){

        Cat.sid = 100;
        Cat mimi = new Cat("mimi");
        mimi.sid = 2000;
        Cat pipi = new Cat("pipi");
        mimi.info();
        pipi.info();
    }
}

Cat.java

package 和 import语句

J2SDK中主要的包介绍

类的继承与权限控制

class Person {
    private String name;
    private int age;
    public void setName(String name) {
        this.name=name;
    }
    public void setAge(int age) {
        this.age=age;
    }
    public String getName(){
        return name;
    }
    public int getAge(){
        return age;
    }
}

class Student extends Person {
    private String school;
    public String getSchool() {
        return school;
    }
    public void setSchool(String school) {
        this.school =school;
    }
}

public class Test {
    public static void main(String arg[]){
        Student student = new Student();
        student.setName("John");
        student.setAge(18);
        student.setSchool("SCH");
        System.out.println(student.getName());
        System.out.println(student.getAge());
        System.out.println(student.getSchool());
    }
}

TestPerson.java

访问控制

public class TestAccess {
}

class T {
    private int i = 0;
                    int j = 0;
    protected int k = 0;
    public int m = 0;

    public void m() {
        i = 9;
    }
}

class TT {
    public void m() {
        T t = new T();
        System.out.println(t.j);
    }
}

TestAccess.java