集合体系概述

 

 

 Collection是单列集合的祖宗，它规定的方法（功能）是全部单列集合都会继承的

public class Work1 {public static void main(String[] args)  {//简单认识一下Collection集合的特点ArrayList<String> list = new ArrayList<>();//有序 可重复 有索引list.add("java1");list.add("java2");list.add("java1");list.add("java2");System.out.println(list);System.out.println(list.get(1));HashSet<String> set = new HashSet<>();//无序 不重复 无索引set.add("java1");set.add("java2");set.add("java1");set.add("java2");set.add("java3");System.out.println(set);}
}

Collection的常用方法

1，public boolean add(E e):添加元素，添加成功返回true

Collection<String> c = new ArrayList<>();//多态写法c.add("java1");c.add("java1");c.add("java2");c.add("java2");c.add("java3");System.out.println(c);//[java1,java1,java2,java2,java3]

2，public void clear():清空集合的元素

        c.clear();System.out.println(c);//[]

3，public boolean isEmpty():判断集合是否为空，是空返回true，反之

System.out.println(c.isEmpty());//flase

4，public int size():获取集合的大小

System.out.println(c.size());//5

5，public boolean contains(Objects obj):判断集合中是否包含某个元素

System.out.println(c.contains("java1"));//true

6，public boolean remove(E e):删除某个元素，删除成功返回true ：如果有多个重复元素默认删除前面的第一个！

System.out.println(c.remove("java1"));
System.out.println(c);//[java1,java2,java2,java3]

7，public Object[] toArray():把集合转换成数组

        Object[] arr = c.toArray();//把集合转换成数组System.out.println(Arrays.toString(arr));//转化成指定类型的数组形式String[] arr1 = c.toArray(new String[c.size()]);System.out.println(Arrays.toString(arr1));

8，把一个集合的全部数据倒入到另一个集合中去

        Collection<String> c1 = new ArrayList<>();c1.add("java1");c1.add("java2");Collection<String> c2 = new ArrayList<>();c2.add("java3");c2.add("java4");c1.addAll(c2);//把c2集合的全部数据倒入(拷贝)到c1集合中去System.out.println(c1);//[java1, java2, java3, java4]System.out.println(c2);//[java3, java4]

Collection的遍历方式

 

迭代器  遍历数组

迭代器概述：迭代器是用来遍历集合的专用方式（数组没有迭代器），在Java中迭代器的代表是Iterator

import java.util.*;public class Work1 {public static void main(String[] args)  {Collection<String> c = new ArrayList<>();//多态写法c.add("赵敏");c.add("小昭");c.add("素素");c.add("灭绝");System.out.println(c);//使用迭代器遍历数组//1，从集合中获取迭代器对象Iterator<String> it = c.iterator();//2,使用循环结合迭代器遍历集合while (it.hasNext()){String ele = it.next();System.out.println(ele);}}
}

增强for循环  遍历数组

 

即能遍历循环，又能遍历数组

import java.util.*;public class Work1 {public static void main(String[] args)  {Collection<String> c = new ArrayList<>();//多态写法c.add("赵敏");c.add("小昭");c.add("素素");c.add("灭绝");System.out.println(c);//增强for遍历集合for (String ele : c){System.out.println(ele);}System.out.println("..............................");//增强for循环遍历数组String[] names = {"简隋英","李玉","洛羿","温小辉"};for (String name:names){System.out.println(name);}}
}

Lambda表达式  遍历集合

 

import java.util.*;
import java.util.function.Consumer;public class Work1 {public static void main(String[] args)  {Collection<String> c = new ArrayList<>();//多态写法c.add("娘娘腔");c.add("附加遗产");c.add("你却爱着一个傻逼");c.add("职业替身");System.out.println(c);c.forEach(new Consumer<String>() {@Overridepublic void accept(String s) {System.out.println(s);}});}
}

 

 

 

案例：遍历集合中的自定义对象

        需求：展示多部小说信息

        分析：1，每本小说都是一个对象，多部小说要使用集合装起来

                   2，遍历集合中的三个小说对象，输出每部电影的详情信息

import java.util.*;public class Work1 {public static void main(String[] args)  {Collection<movie> movies = new ArrayList<>();//往集合中添加对象.................................movies.add(new movie("《人鱼陷落》",9.5,"兰波"));movies.add(new movie("《德萨罗人鱼》",9.3,"德萨罗"));movies.add(new movie("《垂耳执事》",9.5,"言逸"));System.out.println(movies);//使用 增强for循环 遍历集合..........................for (movie m : movies) {System.out.println("名称："+m.getName());System.out.println("评分:"+m.getScore());System.out.println("人物:"+m.getActor());}}
}
class movie{private String name;private double score;private String actor;public movie() {}public movie(String name, double score, String actor) {this.name = name;this.score = score;this.actor = actor;}public String getName() {return name;}public void setName(String name) {this.name = name;}public double getScore() {return score;}public void setScore(double score) {this.score = score;}public String getActor() {return actor;}//重写toString方法....................@Overridepublic String toString() {return "movie{" +"name='" + name + '\'' +", score=" + score +", actor='" + actor + '\'' +'}';}
}