面向對象

類

對象

識別類

類之間的關係

表達類關係的UML符號

構造器

顯示參數和隱式參數

封裝的好處

public class Employee {

    public static int nextId = 0;
    private String name;
    private double salary;
    private Date hireDate;

    public Employee(String n, double s) {
        name = n;
        salary = s;
        hireDate = new Date();
    }

    public String getName() {
        return name;
    }

    public double getSalary() {
        return salary;
    }


    public Date getHireDate() {
        return (Date) hireDate.clone();
    }

    public void raiseSalary(double byPercent) {
        double raise = salary * byPercent / 100;
        salary += raise;
    }

    public static int getNextId() {
        return nextId;
    }

}

不要返回編寫引用可變對象的訪問器方法

Test.class

public class Test {

    public static void main(String[] args) {
        Employee harry = new Employee("周杰倫",8800.0);
        SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
        Date d = harry.getHireDate();
        System.out.println(sdf.format(d));
        d.setTime(d.getTime() + 24 * 60 * 60 * 1000);
        Date d2 = harry.getHireDate();
        System.out.println(sdf.format(d2));
    }
}

結果：

2017-12-12 22:31:57
2017-12-13 22:31:57

修改成：

public Date getHireDate() {
    return (Date) hireDate.clone();
}

final實例域

靜態

靜態域

Employee harry = new Employee("Harry", 16000.0);
harry.nextId = 10;
Employee tom = new Employee("Tom", 13000.0);
tom.nextId = 20;
System.out.println(harry.nextId); //20
System.out.println(tom.nextId); //20
System.out.println(Employee.nextId); //20

靜態方法

輸出

PrintStream ps = new PrintStream("D:\\file.txt");
System.setOut(ps);
System.out.println("HelloWorld");

讀取

InputStream is = new FileInputStream("D:\\file.txt");
System.setIn(is);
Scanner sc = new Scanner(System.in);
StringBuilder builder = new StringBuilder();
while(sc.hasNext()){
    builder.append(sc.nextLine()+"\n");
}
System.out.println(builder.toString());

方法參數

重載

默認域初始化

無參構造器

有參構造器

類設計技巧