聚合（has-A)示例

//Date类 public class Date { private int month; private int day; private int year; public Date(int theMonth,int theDay,int theYear){ month = checkMonth(theMonth); year = theYear; day = checkDay(theDay); System.out.println("Data object constructor for date"+ toDateString()); } private int checkMonth(int testMonth){ if (testMonth > 0 && testMonth <= 12) return testMonth; else{ System.out.println("Invalid month("+ testMonth +")set to 1"); return 1; } } private int checkDay(int testDay){ int daysPerMonth[] = {0,31,28,30,31}; if(testDay >0 && testDay <= daysPerMonth[month]) return testDay; if(month ==2 && testDay ==29 && (year %400 ==0 || (year %4 ==0 && year %100 != 0))) return testDay; System.out.println("Invalid day ("+ testDay +")set to 1"); return 1; } public String toDateString() { return month + "/" + day + "/" + year; } } //Employee类中应用Date类 public class Employee { private String firstName; private String lastName; private Date birthDate; private Date hireDate; public Employee(String first,String last,Date dateofBirth,Date dateofHire) { firstName = first; lastName = last; birthDate = dateofBirth; hireDate = dateofHire; } public String toEmployeeString() { return lastName + "," + firstName + " Hired:" + hireDate.toDateString()+ "Birthday:"+birthDate.toDateString(); } } //程序入口 import javax.swing.JOptionPane; public class EmployeeTest { public static void main(String[] args) { Date birth = new Date(7,24,1949); Date hire = new Date(3,12,1988); Employee employee = new Employee("Bob","Jones",birth,hire); JOptionPane.showMessageDialog(null,employee.toEmployeeString(),"Testing Class Employee",JOptionPane.INFORMATION_MESSAGE); System.exit(0); } }

（编辑：李大同）

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