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!");
        }
    }

}