Java笔记 - 集合框架

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所有集合的父类是Collection

1、add方法的参数类型是Object，以便于接受任意类型对象

2、集合中储存的都是对象的引用（地址）

package collection;import java.util.*;public class CollectionDemo {public static void main(String[] args){method_1();method_2();method_get();}public static void method_1(){ArrayList al = new ArrayList();al.add("a1");al.add("a2");al.add("a3");sop(al); //[[a1,a2,a3]al.remove("a3"); sop(al);//[a1,a2]sop(al.size()); //2sop(al.contains("a1")); //trueal.clear();sop(al); // []sop(al.isEmpty()); //true}public static void method_2(){ArrayList a1 = new ArrayList();ArrayList a2 = new ArrayList();a1.add("a1");a1.add("a2");a1.add("a3");a2.add("a2");a2.add("a3");a2.add("a4");//a1.retainAll(a2); //取交集a1 = [a2,a3]//a1.removeAll(a2); //去重复 a1 = [a1]sop(a1);}public static void method_get(){ArrayList al = new ArrayList();al.add("a1");al.add("a2");al.add("a3");Iterator it = al.iterator();while( it.hasNext() ){sop(it.next());}//a1, a2, a3}public static void sop(Object o){System.out.println(o);} }

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