线程管理

/*
* 把一个线程交给另一个线程称：上下文切换。
* 如果处理器自愿放开处理器控制权，称为：协同式多任务，如果不这样，会造成其他挂起。
* 更多的是采用抢占式线程管理，这种优点：一是能防止单个线程单独占用处理器，二是程序员无需负责上下文切换，
* 而将责任交给操作系统
*/

/*
* 下面实例演示两个账号转账，但条件是必需保持平衡。有竞争条件一定要注意，下面可能实例不正确，但大部分情况下是正确的。
* 这样原因是线程切换时问题。在后面我们会改下。
*
*
*/
package lession3;
import java.text.*;
import java.util.*;
public class AccountManager {
protected CustomerAccount savings;
protected CustomerAccount checking;

public final static int SAVINGS_ACCOUNT=1;
public final static int CHECKING_ACCOUNT=2;
public static void main(String args[]){
int transfers=1000000;
try{
transfers=Integer.parseInt(args[0]);

}catch(Exception e){}
AccountManager am=new AccountManager(transfers);
}

public AccountManager(int transfers){
savings=new CustomerAccount(SAVINGS_ACCOUNT,1000);
checking=new CustomerAccount(CHECKING_ACCOUNT,1000);
NumberFormat formatter=NumberFormat.getCurrencyInstance(Locale.US);
System.out.println("Total balance before thansfers:"+formatter.format(savings.getBalance()+checking.getBalance()));

TransferManager tm1=new TransferManager(checking,savings,transfers);
TransferManager tm2=new TransferManager(checking,savings,transfers);

Thread t1=new Thread(tm1);
Thread t2=new Thread(tm2);
//
t1.start();
t2.start();
try{
t1.join();
t2.join();
}catch(Exception e){

}
System.out.println("Total balance after transfers:"+formatter.format(savings.getBalance()+checking.getBalance()));
}

}

//管理账号类
class TransferManager implements Runnable{
    protected CustomerAccount fromAccount;
    protected CustomerAccount toAccount;
    protected int transferCount;
    public TransferManager(CustomerAccount fromAccount,CustomerAccount toAccount ,int transfers){
    this.fromAccount=fromAccount;
    this.toAccount=toAccount;
    this.transferCount=transfers;
    }
public void run() {
double balance;
double transferAmount;
for(int i=0;i<transferCount;i++){
balance=fromAccount.getBalance();
transferAmount=(int)(balance*Math.random());
balance-=transferAmount;
fromAccount.setBalance(balance);
balance=toAccount.getBalance();
balance+=transferAmount;
toAccount.setBalance(balance);
}


}

}
//账号类
class CustomerAccount{
protected int accountType;
protected double balance;
public CustomerAccount(int type,double balance){
this.accountType=type;
this.balance=balance;
}
public int getAccountType() {
return accountType;
}
public double getBalance() {
return balance;
}
public void setBalance(double balance) {
this.balance = balance;
}

}