迭代器Iterator操作及底层实现

Iterator使用

package com.gcx.demo;import java.util.ArrayList;import java.util.HashMap;import java.util.HashSet;import java.util.Iterator;import java.util.List;import java.util.Map;import java.util.Set;public class IteratorTest {public static void main(String[] args) {List list=new ArrayList();list.add("a");list.add("b");Iterator iterator = list.iterator();while(iterator.hasNext()){Object next = iterator.next();System.out.println(next);}Set set = new HashSet();set.add("高1");set.add("高2");set.add("高3");for(Iterator it=set.iterator();it.hasNext();){Object next = it.next();System.out.println(next);}Map map = new HashMap();map.put("aa", "aaaa");map.put("bb", "bbbb");Set keySet = map.keySet();Iterator iterator2 = keySet.iterator();while(iterator2.hasNext()){Object next = iterator2.next();System.out.println(next);}}}

底层实现

package com.gcx.demo;import java.util.Arrays;import java.util.Iterator;public class IteratorImpl<e> implements java.lang.Iterable<e>{private Object elem[]=new Object[5];private int size=0;public int size(){return size;}public void add(E ele){if(this.size==elem.length){elem=Arrays.copyOf(elem, elem.length+5);} elem[size++]=ele;}public Iterator<e> iterator(){return new Iterator<e>(){private int cursor=-1;@Overridepublic boolean hasNext() {return cursor+1<size;}@Overridepublic E next() {cursor++;return (E)elem[cursor];}public void remove(){System.arraycopy(elem, cursor+1, elem, cursor, size-(cursor+1));size--;cursor--;}};}public static void main(String[] args) {IteratorImpl<integer> iter=new IteratorImpl<>();iter.add(1);iter.add(2);for(Integer i:iter){System.out.println(i);}System.out.println("********");IteratorImpl<string> iter2=new IteratorImpl<>();iter2.add("aaa");iter2.add("aaa1");iter2.add("aaa2");iter2.add("aaa3");Iterator<string> iterator = iter2.iterator();while(iterator.hasNext()){String next = iterator.next();System.out.println(next);}}} </string></string></integer></e></e></e></e>