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(size==element.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 size==0;
  }
  //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(id==cards[i].getId()&&passwd==cards[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;
               }
           }