java笔记 泛型细节

泛型的使用细节

1. 给泛型指向的数据类型要求是引用类型,不能是基本数据类型

2.在给泛型指定具体类型后,可以传入类型或者其子类类型

3.泛型使用形式


泛型课堂练习

import java.util.ArrayList;
import java.util.Comparator;

public class TestGeneric03 {
    public static void main(String[] args) {
        ArrayList employees = new ArrayList<>();
        employees.add(new Employee("jerry",22000,new MyDate(1,28,1995)));
        employees.add(new Employee("tom",20000,new MyDate(3,20,1996)));
        employees.add(new Employee("jean",22000,new MyDate(9,2,1994)));

        employees.sort(new Comparator() {
            @Override
            public int compare(Employee emp1, Employee emp2) {
                //先按照name排序,如果name相同,则按生日日期的先后排序
                //先对传入的参数进行验证
                if (!(emp1 instanceof Employee && emp2 instanceof Employee)){
                    System.out.println("类型不正确...");
                    return 0;
                }
                //比较name
                int i = emp1.getName().compareTo(emp2.getName());
                if ( i != 0){
                    return i;
                }
                //下面是对birthday的比较,因此我们最好把这个比较,放在MyDate类方法
                //封装后,将来可维护性和复用性就大大增加
                return emp1.getBirthday().compareTo(emp2.getBirthday());
            }
        });
        System.out.println("对雇员进行排序后");
        System.out.println("employees = " + employees);
    }
}

public class MyDate implements Comparable{
    private int month;
    private int day;
    private int year;

    public MyDate(int month, int day, int year) {
        this.month = month;
        this.day = day;
        this.year = year;
    }

    @Override
    public String toString() {
        return "MyDate{" +
                "month=" + month +
                ", day=" + day +
                ", year=" + year +
                '}';
    }

    public int getMonth() {
        return month;
    }

    public void setMonth(int month) {
        this.month = month;
    }

    public int getDay() {
        return day;
    }

    public void setDay(int day) {
        this.day = day;
    }

    public int getYear() {
        return year;
    }

    public void setYear(int year) {
        this.year = year;
    }

    @Override
    public int compareTo(MyDate o) {
        int yearMinus = year - o.getYear();
        if (yearMinus != 0) {
            return yearMinus;
        }
        //如果year相同,比较month
        int monthMinus = month - o.getMonth();
        if (monthMinus != 0) {
            return monthMinus;
        }
        return day - o.getDay();
    }
}

public class Employee {
    private String name;
    private double sal;
    private MyDate birthday;

    @Override
    public String toString() {
        return "nEmployee{" +
                "name='" + name + ''' +
                ", sal=" + sal +
                ", birthday=" + birthday +
                '}';
    }

    public Employee(String name, double sal, MyDate birthday) {
        this.name = name;
        this.sal = sal;
        this.birthday = birthday;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public double getSal() {
        return sal;
    }

    public void setSal(double sal) {
        this.sal = sal;
    }

    public MyDate getBirthday() {
        return birthday;
    }

    public void setBirthday(MyDate birthday) {
        this.birthday = birthday;
    }
}