创建类

提示

• 前置阅读 Objects, Classes, Interfaces, Packages, and Inheritance
• Creating Classes

声明类

Bicycle.java

public class Bicycle {
    public int cadence;
    public int gear;
    public int speed;

    public Bicycle(int startCadence, int startSpeed, int startGear) {
        cadence = startCadence;
        gear = startGear;
        speed = startSpeed;
    }

    public void setCadence(int newValue) {
        cadence = newValue;
    }

    public void setGear(int newValue) {
        gear = newValue;
    }

    public void applyBrake(int decrement) {
        speed -= decrement;
    }

    public void speedUp(int increment) {
        speed += increment;
    }
}

MountainBike.java

public class MountainBike extends Bicycle {

    public int seatHeight;

    public MountainBike(int startHeight, int startCadence,
                        int startSpeed, int startGear) {
        super(startCadence, startSpeed, startGear);
        seatHeight = startHeight;
    }

    public void setHeight(int newValue) {
        seatHeight = newValue;
    }
}

• 子类只能有一个父类
• 一个类可以实现多个接口

声明成员变量

• 类中的成员变量称为成员变量
• 方法或代码块中的变量称为局部变量
• 方法声明中的变量称为参数

public class Bicycle {

    // 成员变量，称为字段
    public int cadence;
    public int gear;
    public int speed;

    // 方法声明中的变量，称为参数
    public void setCadence(int newValue) {
        // 局部变量
        int temp;

        // ...
    }
}

私有字段

• 字段通常是私有的
• 可以通过方法访问字段

public class Bicycle {

    private int cadence;
    private int gear;
    private int speed;

    public Bicycle(int startCadence, int startSpeed, int startGear) {
        gear = startGear;
        cadence = startCadence;
        speed = startSpeed;
    }

    public int getCadence() {
        return cadence;
    }

    public int getGear() {
        return gear;
    }

    public int getSpeed() {
        return speed;
    }

}