例題: BangBuck.java (原始碼)
class Product {
public Product() { ... }
public void read() { ... }
public boolean isBetterThan(Product b) { ... }
public void print() { ... }
implementation detail
}
方法中有三類:
class Product{
public Product();
public void read();
public boolean isBetterThan(Product b);
public void print();
private String name;
private double price;
private int score;
}
public Product()
{ name = "";
price = 0;
score = 0;
}
public Employee() { name = ""; salary = 0; }
public Employee(String n, double s) { name = n; salary = s; }
預設的建構器沒有參數，另一建構器有兩個參數。 凡是兩個函數有相同名稱，但不同型式的參數，稱為 overloaded。
假如一類別的資料項為一物件，如
class Employee {
public Employee(String employeeName,
int hireYear, int hireMonth, int hireDay) { ... }
. . .
private String name;
private double salary;
private Time hireDate;
}
hireDate 是屬於類別 Time 的物件。
在 Employee 的建構器中，設定 hireDate 的初值時，用 Time 的建構器， 如
public Employee(String employeeName,
int hireYear, int hireMonth, int hireDay) {
name = employeeName;
salary = 0;
hireDate = new Time(hireYear, hireMonth, hireDay, 0, 0, 0);
}
例如， raiseSalary 不能直接讀寫 salary (類別 Employee 的私有資料):
static void raiseSalary(Employee e, double percent) {
e.salary = e.salary * (1 + percent/100); // error
}
而必須使用 getSalary 和 setSalary (均為類別
Employee
的公用方法):
static void raiseSalary(Employee e, double percent) {
double newSalary = e.getSalary() * (1 + percent/100);
e.setSalary(newSalary);
}
static void raiseSalary(Employee e, double percent) {
double newSalary = e.getSalary() * (1 + percent/100);
e.setSalary(newSalary);
}
假設 harry 是類別 Employee 的物件，調薪用
raiseSalary(harry, 7);
改寫 raiseSalary 為個例方法:
class Employee {
public void raiseSalary(double percent) {
salary = salary * (1 + percent/100);
}
}
調薪必須用
harry.raiseSalary(7);