Java之路 - final、内部类、Object、Date、Calendar

final MyClass c1 = new MyClass("chris");
c1 = new MyClass("joe"); //！！！！错误写法
c1.setName（"joe"）; //这种是可行的 对其内容是可以改变

public class MyClass {
    private final String name;

    public MyClass() {
        name = "chris";
    }
    public MyClass(String name) {
        this.name = name;
    }

    public String getName() {
        return name;
    }
}

public class MyDemoFinal {
    public static void main(String[] args) {
      Body body = new Body();
      body.methodBody();//通过调用外部类方法使用内部类方法
      //直接访问成员内部类  
      Body.heart directUse = new Body().new heart();
      directUse.methodHeart();
    }
}

public class Outer {
    int num = 10; //外部类成员变量
    public class Inner{
        int num = 20; //内部类成员变量
        public void methodInner(){
            int num = 30; //内部类方法的局部变量
            System.out.println(num); //输出的是局部变量
            System.out.println(this.num); //输出的是内部类成员变量
            System.out.println(Outer.this.num);//外部类的成员变量
        }
    }
}

public class Outer {
    public void methodOuter(){
        class Inner { //这是个局部内部类
            int num = 10;
            public void methodInner(){
                System.out.println(num);
            }
        }
    Inner in = new Inner();
        in.methodInner();
    }
}

public class Outer {
    public void methodOuter(){
        int num = 10;
        class Inner { //这是个局部内部类
            public void methodInner(){
                System.out.println(num);
            }
        }
    }
}

匿名内部类的匿名对象用法
new MyInterface() {
            @Override
            public void methodAbs1() {
                System.out.println("1111");
            }

            @Override
            public void methodAbs2() {
                System.out.println("2222");

            }
        }.methodAbs1();

public class DemoOtherClass {
    public static void main(String[] args) {
        Person p = new Person("chris",21);
        String s = p.toString();
        System.out.println(s);
        System.out.println(p);
    }
}

public class Person {
    private String name;
    private int age;

    public Person() {

    }
    public Person(String name, int age) {
        this.name = name;
        this.age = age;
    }

    @Override
    public String toString() {
        return "Person{" +
                "name=‘" + name + ‘\‘‘ +
                ", age=" + age +
                ‘}‘;
    }

public boolean equals(Object obj) {
        return (this == obj);
    }

public class DemoOtherClass {
    public static void main(String[] args) {
        Person p1 = new Person("chris",21);
        Person p2 = new Person("joe",20);
        boolean result = p1.equals(p2);
        System.out.println(result);
        System.out.println(p1.equals(p2));

    }
}

@Override
    public boolean equals(Object obj){
        //增加一个判断，如果传过来的参数obj是this本身，直接返回true
        if(obj == this){
            return true;
        }

        //增加一个判断，如果传过来的参数为null，直接返回false,提高程序的效率
        if (obj == null){
            return false;
        }
        //先增加一个判断，判断obj是否是person类型才能转换，比如random，可以防止ClassCastException
        if (obj instanceof Person){
            //使用向下转型
            Person p = (Person) obj;
            //比较两个对象的属性;一个是调用方法的this（p1），一个是p（obj=p2） 此时在使用字符串方法中的equals方法来比较
            boolean b = this.name.equals(p.name) && this.age == p.age;
            return b;
        }
        //不是Person类型，就直接返回false
        return false;
    }

public static boolean equals(Object a, Object b) {
        return (a == b) || (a != null && a.equals(b));
    }

public class DemoOtherClass {
    public static void main(String[] args) {
        System.out.println(System.currentTimeMillis());//获取当前系统时间到时间原点经历了多少毫秒
        methodDate(); 
    }
    public static void methodDate(){　　
        Date date = new Date();
        System.out.println(date);
    }
}

public static void methodDate(){
        Date date1 = new Date();
        System.out.println(date1);
        Date date2 = new Date(0L);
        System.out.println(date2);
    }

public class CalendarPratise {
    public static void main(String[] args) {
        Date data = new Date();
        System.out.println(data.toLocaleString());  //当前电脑下的时间
    }
}

private static void demo01() {
        SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH-mm-ss");
        Date data = new Date();
        String timeText = sdf.format(data);
        System.out.println(data);
        System.out.println(timeText);  //输出的是按照构造方法中指定的模式的字符串
    }

private static void demo01() throws ParseException {
        SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH-mm-ss");
        Date date = sdf.parse("2020-04-16 13-28-08");
        System.out.println(date);
    }

public class DatePratise {
    public static void main(String[] args) throws ParseException {
        Scanner s = new Scanner(System.in);
        System.out.println("请输入您的生日,格式为yyyy-MM-dd");
        String birthday = s.next();
        //将获取的生日解析为Date格式
        SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");
        Date dateBirthday = sdf.parse(birthday);
        //将Date转换为毫秒值
        long seconds = dateBirthday.getTime();
        //获取当前的日期转换为毫秒值
        Long timeNow = new Date().getTime();
        //两个时间相减 now - past
        long time = timeNow - seconds;
        //将差值转换为天 (s/1000/60/60/24)
        System.out.println("你已经出生了" + time/1000/60/60/24 +"天");


    }
}

public class CalendarPratise {
    public static void main(String[] args) {
        Calendar calendar = Calendar.getInstance(); //多态
        int year = calendar.get(Calendar.YEAR);
        System.out.println(year);
        int month = calendar.get(Calendar.MONTH);
        System.out.println(month); //西方的月份为0-11月 所以我们要加一个月
        int date = calendar.get(Calendar.DATE);
        System.out.println(date);
    }
}

public class CalendarPratise {
    public static void main(String[] args) {
        Calendar calendar = Calendar.getInstance(); //多态
        calendar.set(Calendar.YEAR,2050);
        calendar.set(2012,3,4); //重载方法同时对三个值进行设置
    }
}

public class CalendarPratise {
    public static void main(String[] args) {
        Calendar calendar = Calendar.getInstance(); //多态
        calendar.add(Calendar.YEAR,2);//将年份增加两年
    }
}

public class CalendarPratise {
    public static void main(String[] args) {
        Calendar calendar = Calendar.getInstance(); //多态
        Date time = calendar.getTime();
        System.out.println(time);
    }
}