目录
- Math
- Random
- Date
- Carlendar
- DateFormat
- SimpleDateFoemat
- Comparator
- Clone
Math
System.out.println("PI的值："+Math.PI);
System.out.println("-10的绝对值："+Math.abs(-10));
System.out.println("Math.random()="+Math.random());
System.out.println("Math.round(98.56)="+Math.round(98.568977d));
System.out.println("Math.round(88.56789)="+Math.round(88.56789*100)/100.0);
System.out.println("Math.sqrt(2d)="+Math.sqrt(2d));
Random
//随机数
Random r = new Random();
int x = r.nextInt(100);
System.out.println("x="+x);
Date
//创建了一个日期对象
Date date = new Date();
System.out.println("当前时间的毫秒："+date.getTime());
System.out.println(date);
Calendar
Calendar c = Calendar.getInstance();
// Calendar c = new GregorianCalendar();
int year = c.get(Calendar.YEAR);//年
int month = c.get(Calendar.MONTH);//月
int day = c.get(Calendar.DAY_OF_MONTH);//日
int hour = c.get(Calendar.HOUR_OF_DAY);//时
int minute = c.get(Calendar.MINUTE);//分
int second = c.get(Calendar.SECOND);//秒
int millisecond = c.get(Calendar.MILLISECOND);//毫秒
//星期
String[] weeks = {"星期日","星期一","星期二","星期三","星期四","星期五","星期六"};
int week = c.get(Calendar.DAY_OF_WEEK);
StringBuilder sb = new StringBuilder();
sb.append(year).append("年").append(month).append("月").append(day).append("日 ")
.append(hour).append(":").append(minute).append(":").append(second).append(" ")
.append(millisecond).append(" ").append(weeks[week]);
System.out.println(sb.toString());
DateFormat
// DateFormat df = DateFormat.getDateInstance();
//参数（指定日期风格，指定语言环境）
// DateFormat df = DateFormat.getDateInstance(DateFormat.LONG, Locale.CHINA);
// DateFormat df = DateFormat.getTimeInstance();
DateFormat df = DateFormat.getTimeInstance(DateFormat.LONG, Locale.getDefault());
String nowDate = df.format(new Date());
System.out.println("当前日期为："+nowDate);
SimpleDateFormat
//用默认的模式和默认语言环境的日期格式符号构造 SimpleDateFormat。
// SimpleDateFormat sdf = new SimpleDateFormat();
SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss SSS");
String s = sdf.format(new Date());
System.out.println(s);
Comparator
/**
* 人类
* 如果自定义类的对象要实现排序（比较）,那么就要实现Comparable接口，并实现接口的
* compareTo方法
*/
public class Person implements Comparable<Person>{
private String name;
private int age;
public Person() {
}
public Person(String name, int age) {
this.name = name;
this.age = age;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
@Override
public String toString() {
return "Person [name=" + name + ", age=" + age + "]";
}
//比较器的比较方法
//如果当前对象小于参数对象，返回-1
//如果当前对象等于参数对象，返回0
//如果当前对象大于参数对象，返回1
@Override
public int compareTo(Person o) {
//实现：定义对象之间的比较规则
if(o==null){
throw new NullPointerException();
}
if(this.age<o.age){
return -1;
}else if(this.age>o.age){
return 1;
}
return 0;
}
}
/**
* 人类*/
public class Person2{
private String name;
private int age;
public Person2() {
}
public Person2(String name, int age) {
this.name = name;
this.age = age;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
@Override
public String toString() {
return "Person [name=" + name + ", age=" + age + "]";
}
}
/**
* 自定义的类比较器
*/
public class Person2Comparator implements Comparator<Person2>{
@Override
public int compare(Person2 o1, Person2 o2) {
if(o1==null || o2==null){
throw new NullPointerException();
}
if(o1.getAge()<o2.getAge()){
return -1;
}else if(o1.getAge()>o2.getAge()){
return 1;
}
return 0;
}
}
//对象的排序
public class PersonSortDemo {
public static void main(String[] args) {
String[] names = {"张三","李四","王五","刘备","张飞","关羽"};
Person[] persons = {
new Person("张三", 27), new Person("李四", 29),
new Person("王五", 41), new Person("刘备", 33),
new Person("张飞", 25), new Person("关羽", 30) };
Person2[] persons2 = {
new Person2("张三", 27), new Person2("李四", 29),
new Person2("王五", 41), new Person2("刘备", 33),
new Person2("张飞", 25), new Person2("关羽", 30) };
Arrays.sort(names);
System.out.println(Arrays.toString(names));
//自定义类对象数组排序
Arrays.sort(persons);
System.out.println(Arrays.toString(persons));
//使用自定义的比较器
Arrays.sort(persons2, new Person2Comparator());
System.out.println(Arrays.toString(persons2));
}
}
Clone
/**
* 一个类要想实现克隆功能，必须：
* 1、实现Cloneable接口，该接口是一个标记接口
* 2、重写Object类中的clone方法
*/
public class Cat implements Cloneable{
private String name;
private int age;
public Cat(String name, int age) {
super();
this.name = name;
this.age = age;
}
public Cat() {
super();
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
@Override
public String toString() {
return "Cat [name=" + name + ", age=" + age + "]";
}
//重写Object的clone方法
@Override
protected Object clone() throws CloneNotSupportedException {
return super.clone();
}
}
//要创建一组类似的对象，那么从性能上考虑，就可以使用克隆技术
public class Test {
public static void main(String[] args) {
Cat c = new Cat("张三",3);
System.out.println("c="+c);
try {
Cat c1 = (Cat)c.clone();
System.out.println("c1="+c1);
} catch (CloneNotSupportedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
我是天王盖地虎的分割线
时间： 2024-12-26 14:26:05