java（集合遍历）

import java.util.ArrayList; import java.util.HashMap; import java.util.HashSet; import java.util.Iterator; import java.util.Map; import java.util.Set; public class CollectionTest { public static void main(String[] args) { //ArrayList遍历 ArrayList<Object> arrayList= new ArrayList<Object>(); arrayList.add("123"); arrayList.add(456); arrayList.add(true); arrayList.add('a'); System.out.println(arrayList); //打印结果：[123, 456, true, a] //方式一 for (Object object : arrayList) { System.out.println(object); } //打印结果： 123 // 456 // true // a //方式二 for (int i = 0; i < arrayList.size(); i++) { System.out.println(arrayList.get(i)); } //方式三 Iterator<Object> iterator=arrayList.iterator(); while(iterator.hasNext()) { System.out.println(iterator.next()); } //方式四 for (int i = 0; i < arrayList.size(); i++) { System.out.println(arrayList.get(i)); } //set集合无序的、不可重复的 Set<Object> set = new HashSet<>(); set.add("abc"); set.add("666"); set.add(777); // set.add(666); System.out.println(set); for (Object object : set) { System.out.println(object); } //打印结果： 123 // 456 // true // a //方式二 Iterator<Object> iterator=set.iterator(); while(iterator.hasNext()) { System.out.println(iterator.next()); } //Map 无序的 Person p1=new Person(11, "zhangsan"); Person p2=new Person(11, "lisi"); Map<String, Person> map =new HashMap<String, Person>(); map.put(p1.name, p1); map.put(p2.name, p2); //System.out.println(map); Set<String> set1= map.keySet(); Iterator<String> iterator1=set1.iterator(); while(iterator1.hasNext()) { System.out.println(map.get(iterator1.next())); } } } class Person{ int age ; String name ; public Person(int age, String name) { super(); this.age = age; this.name = name; } @Override public int hashCode() { final int prime = 31; int result = 1; result = prime * result + age; result = prime * result + ((name == null) ? 0 : name.hashCode()); return result; } @Override public boolean equals(Object obj) { if (this == obj) return true; if (obj == null) return false; if (getClass() != obj.getClass()) return false; Person other = (Person) obj; if (age != other.age) return false; if (name == null) { if (other.name != null) return false; } else if (!name.equals(other.name)) return false; return true; } @Override public String toString() { return "Person [age=" + age + ", name=" + name + "]"; } }