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[Java教程]Java Iterator, ListIterator 和 foreach语句使用


Java Iterator, ListIterator 和 foreach语句使用

foreach语句结构: 
for(part1:part2){part3}; 
part2 中是一个数组对象,或者是带有泛性的集合. 
part1 定义了一个局部变量,这个局部变量的类型与part2中的对象元素的类型是一致的. 
part3 当然还是循环体.

foreach语句是java5的新特征之一,在遍历数组、集合方面,foreach为开发人员提供了极大的方便。 foreach语句是for语句的特殊简化版本,但是foreach语句并不能完全取代for语句,然而,任何的foreach语句都可以改写为for语句版本。 foreach并不是一个关键字,习惯上将这种特殊的for语句格式称之为“foreach”语句。从英文字面意思理解foreach也就是“for 每一个”的意思。实际上也就是这个意思。  

package com.twzheng;import java.util.Iterator;import java.util.ListIterator;import java.util.LinkedList;import java.util.Scanner;public class MainClass {  private static Scanner scanner;  private static String enterString;  /**   * @param args   */  public static void main(String[] args) {    // TODO Auto-generated method stub    scanner = new Scanner(System.in);        LinkedList<String> myLinkedList = new LinkedList<String>();        printList(myLinkedList);        initialLinkedList(myLinkedList);        System.out.println("findMember -> Please enter member value: ");    enterString = scanner.next();        if(findMember(myLinkedList, enterString)){      System.out.println(enterString + " is in the linkedList.");    }else{      System.out.println(enterString + " is not found in the linkedList.");    }        printList(myLinkedList);  }
  // Java Iterator 使用 private static void printList(LinkedList<String> linkedList){ System.out.println("======================================"); Iterator<String> itr = linkedList.iterator(); // Iterator .hasNext()判断是否还有下一个 if (itr.hasNext()){ System.out.println("Pint linkedList members:"); }else{ System.out.println("The linkedList is empty!"); } int i = 0; while(itr.hasNext()){
       // Iterator .next()取得下一个 System.out.println(" <" + i + ">" + itr.next()); i++; } System.out.println("^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^"); }
  // Java foreach语句使用 private static boolean findMember(LinkedList<String> linkedList, String lValue){ for(String checkedValue: linkedList){ if(checkedValue.equals(lValue)){ System.out.println("Found " + lValue + " at linkedList<" + linkedList.indexOf(checkedValue) + ">."); return true; } } return false; }
  // Java ListIterator 使用 .next() .previous() .add() private static boolean addMember(LinkedList<String> linkedList, String lValue){ ListIterator<String> ltr = linkedList.listIterator(); while(ltr.hasNext()){ int comp = ltr.next().compareTo(lValue); if(comp == 0){ // equal, do not add System.out.println(lValue + " is already inclued in the linkedList."); return false; } else if(comp > 0){ // new member ltr.previous(); ltr.add(lValue); System.out.println(lValue + " has been added in the linkedList."); return true; } else { // ??? } } ltr.add(lValue); return true; } private static void initialLinkedList(LinkedList<String> linkedList){ System.out.println("Initialize linkedList:"); int choseNumber; boolean stopEnter = false; try { do { System.out.println(" 0 - stop enter "); System.out.println(" 1 - enter a new member "); System.out.println("Please chose number: "); choseNumber = scanner.nextInt(); switch (choseNumber) { case 0: stopEnter = true; break; case 1: System.out.println("Please enter new member value: "); addMember(linkedList, scanner.next()); break; default: System.out.println("Enter error!"); break; } } while (!stopEnter); } catch (Exception e) { // TODO: handle exception System.out.println("Enter error!"); } } }