java.util:
java.util.Date:表示系统当前时间
getTime():获得毫秒数 1970-1-1
System.currentTimeMillis();
Calendar:
实例化方法:
Calendar cal = Calendar.getInstance();
DateFormat sdf = new SimpleDateFormat():
format(Date):--->String
parse(String):--->java.util.Date
Date---Calendar
cal.setTime(Date);---->Calendar
cal.getTime();-----Date
集合:多个元素组成的单个对象
1、集合中可以存放任意类型的元素
2、集合的大小不受限制
数组:
1、数组中只能存放相同类型的数据
2、数组的长度一旦定义,不能修改
public class ArrayList extends AbstractList
implements List{}
import java.util.ArrayList; import java.util.Iterator; public class ArrayListDemo { public static void main(String[] args) { //实例化ArrayList对象 ArrayList<String> list = new ArrayList<>(); //获得集合的大小 System.out.println(list.size()); //判断集合是否为空 System.out.println(list.isEmpty()); //添加元素 list.add("abc"); list.add("xyz"); list.add("xxx"); list.add("abc"); //遍历元素 for(int i = 0;i < list.size();i++){ System.out.println(list.get(i)); } System.out.println("------------------"); //用迭代器迭代元素 Iterator<String> it = list.iterator(); while(it.hasNext()){ String str = it.next(); System.out.println(str); } //清空集合 // list.clear(); // System.out.println(list.size()); list.remove(0); System.out.println(list); } }
package com.newer.cn; import java.util.HashSet; import java.util.Iterator; import java.util.Set; /** * set集合: * 1、不能存放重复元素,其他的集合可以 * 2、默认的按照升序排序 * @author Administrator * */ public class SetDemo { public static void main(String[] args) { Set<Integer> set = new HashSet<Integer>(); set.add(8); set.add(3); set.add(6); set.add(1); set.add(3); Iterator<Integer> it = set.iterator(); while(it.hasNext()){ System.out.println(it.next()); } } }
7、完成下面的要求
1) 创建一个List,在List 中增加三个工人,基本信息如下:
姓名 年龄
工资
zhang3 18 3000
li4 25 3500
wang5
22 3200
2) 在li4 之前插入一个工人,信息为:姓名:zhao6,年龄:24,工资3300
3) 删除wang5 的信息
4) 利用for 循环遍历,打印List 中所有工人的信息
package ch0315hw; public class Employee { private String name; private int age; private double salary; public Employee(){ } public Employee(String name,int age,double salary){ this.name = name; this.age = age; this.salary = salary; } 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; } public double getSalary() { return salary; } public void setSalary(double salary) { this.salary = salary; } public String toString(){ return "姓名:"+name+" 年龄"+age+" 工资:"+salary; } }
package ch0315hw; import java.util.LinkedList; import java.util.List; public class EmoloyeeTest { public static void main(String[] args) { List<Employee> l = new LinkedList<Employee>(); l.add(new Employee("zhang3", 18, 3000)); l.add(new Employee("li4 ", 25, 3500)); l.add(new Employee("wang5", 22, 3200)); System.out.println(l); int index = 0; for (int i = 0; i < l.size(); i++) { Employee e = l.get(i); if (e.getName() == "li4 ") index = i; } l.add(index, new Employee("zhao6", 24, 3300)); System.out.println(l); for (int i = 0; i < l.size(); i++) { Employee e = l.get(i); if (e.getName() == "wang5") index = i; } l.remove(index); System.out.println(l); for (Employee e : l) System.out.println(e); } }