整理最近学习的Java

1. 类和对象的定义

• 访问限定符：
• public(公有的) default(默认包访问权限) protected(保护) private(私有)

2. 对象大小 对象头（8字节（JVM位数有关）） + 实例变量 + 内存填充 （8的倍数）
3. 方法调用设计到的内存结构
4. 类的应用（MyArrayList,ATM机）

• MyArrayList

  public class MyArrayList {
  private int[] element;//定义数组
  private static int size;//有效数组大小
  private final int INITSIZE = 10;//初始化数组长度

  public MyArrayList() {//构造函数初始化成员变量
  element=new int[INITSIZE];
  }

  public void addHead(int value) {
  ensureCapacity();
  //将元素后移一位
  for(int i=size-1;i>=0;i--) {
  element[i+1]=element[i];
  }
  element[0]=value;
  size++;
  }
  //对数组扩容
  private void ensureCapacity() {
  // TODO Auto-generated method stub
  if(sizeelement.length) {
  element=Arrays.copyOf(element,element.length+(element.length>>1));
  }
  }
  //将插入的值赋给末尾元素，长度+1
  public void addTail(int value) {
  ensureCapacity();
  element[size++]=value;
  //size++;
  }
  private boolean isEmpty() {
  return size0;
  }
  //1 2 2 3
  public void removeValue(int value) {

  if(isEmpty()) {
  return;
  }
  for(int i=0;i<size;) {
  if(element[i]==value) {
  for(int j=i+1;j<size-i;j++) {
  element[j-1]=element[j];
  }
  }else {
  i++;
  }
  }

  }

  public void removeHead() {
  if(isEmpty()) {
  return;
  }
  for(int i=1;i<size;i++) {
  element[i-1] = element[i];
  }
  size--;
  }
  /**
  * 去掉尾元素，先判断是否为空，不则直接长度-1
  /
  public void removeTail() {
  if(isEmpty()) {
  return;
  }
  size--;
  }
  /*
  *
  * @param srcValue ֵ 原有值
  * @param aimValue 目标值
  */
  public void change(int srcValue,int aimValue) {
  if(isEmpty()) {
  return;
  }
  for(int i=0;i<size;i++) {
  if(element[i] == srcValue) {
  element[i] = aimValue;
  }
  }
  }
  public boolean contains(int value) {
  for(int i=0;i<size;i++) {
  if(element[i] == value) {
  return true;
  }
  }
  return false;
  }
  public void show() {
  for(int i=0;i<size;i++) {
  System.out.println(element[i]+" ");
  }
  }

• ATM

  /**
  * ATM类
  * 基于当前登录成功的这张卡进行操作
  * 存款，取款，转账，查余额，退卡
  * @author Ray
  *
  */
  public class ATM {
  private Bank bank;
  private static Scanner scanner;

  public ATM() {
  bank = new Bank();
  scanner=new Scanner(System.in);
  }
  private BankCard login(int id,int passwd){
  return bank.contains(id,passwd);
  }
  //注册功能，在银行增加卡是否成功
  private boolean register(int id,int passwd) {

  BankCard card=new BankCard(id,passwd);
  return bank.add(card);

  }

  public void start(){

  while(true) {
  System.out.println("1. 登陆 2.注册 3.退出");
  int choice = scanner.nextInt();
  if(choice == 3){
  break;
  }
  System.out.println("请输入账号密码：");
  int id = scanner.nextInt();
  int passwd = scanner.nextInt();
  BankCard successCard=null;
  switch (choice){
  case 1:
  successCard=login(id,passwd);
  if(successCard != null) {
  System.out.println("登陆成功");
  loginSuccess(successCard);
  }else {
  System.out.println("登陆失败");
  }
  break;
  case 2:
  if(register(id,passwd)) {
  System.out.println("注册成功");
  }else {
  System.out.println("注册失败");
  }

  break;
  }
  }
  }
  private void loginSuccess(BankCard successCard) {
  while(true) {
  System.out.println("1. 存款 2.取款 3.转账 4.余额 5.退卡");
  int choice = scanner.nextInt();
  if(choice == 5){
  break;
  }
  switch(choice) {
  case 1:
  System.out.println("请输入存款金额");
  int money = scanner.nextInt();
  successCard.saveMoney(money);
  System.out.println("存款成功");
  break;
  case 2:
  System.out.println("请输入取款金额");
  money = scanner.nextInt();
  if(successCard.withdrawMoney(money)) {
  System.out.println("取款成功");
  }else {
  System.out.println("取款失败");
  }
  break;
  case 3:
  System.out.println("请输入转账用户名和密码");
  int id=scanner.nextInt();
  int passwd = scanner.nextInt();
  System.out.println("请输入转账金额");
  money = scanner.nextInt();
  BankCard userCard = bank.contains(id, passwd);
  if(userCard != null) {
  if(successCard.withdrawMoney(money)) {//当前卡取款成功
  userCard.saveMoney(money);
  System.out.println("转账成功");
  }else {
  System.out.println("余额不足");
  }
  }else {
  System.out.println("无该用户");
  }

  break;
  case 4:
  System.out.println("余额为："+successCard.getMoney());
  break;

  }
  }
  }

  }

  /**
  *银行类
  **/

  public class Bank {
  private BankCard[] cards;//10
  private int size;//有效用户个数
  private static final int INITSIZE = 10;

  public Bank() {
  cards=new BankCard[INITSIZE];
  //this(INITSIZE)
  }
  public boolean add(BankCard card) {
  //如果之前注册过，增加失败
  if(contains(card.getId(),card.getPasswd()) != null) {
  return false;
  }
  if(size == cards.length) {//数组已满，扩容
  cards = Arrays.copyOf(cards, cards.length);
  }
  cards[size] = card;
  size++;
  return true;
  }
  public BankCard contains(int id, int passwd) {
  // TODO Auto-generated method stub
  BankCard card = null;
  for(int i=0;i<size;i++) {
  if(idcards[i].getId()&&passwdcards[i].getPasswd()) {
  card = cards[i];
  break;
  }

  }
  return card;
  }
  }

  /**
  * 银行卡类
  * @author Ray
  *
  */
  public class BankCard {
  private int id;
  private int passwd;
  private int money;

  public BankCard(int id,int passwd) {
  this.id=id;
  this.passwd=passwd;
  }

  public int getId() {
  return id;
  }

  public int getPasswd() {
  return passwd;
  }

  public int getMoney() {
  return money;
  }
  public void saveMoney(int money) {
  // TODO Auto-generated method stub
  this.money+=money;
  }

  public boolean withdrawMoney(int money) {
  boolean flag = false;
  // TODO Auto-generated method stub
  if(this.money >= money) {
  this.money -= money;
  flag = true;
  }
  return flag;
  }
  }