class Allocator{
    //通過破壞占有且等待條件避免死鎖現(xiàn)象的發(fā)生
    private List<Object> als = new ArrayList<>();
    //一次申請(qǐng)所有的資源
    synchronized boolean apply(Object from, Object to){
      if (als.contains(from) || als.contains(to)){
        //只要存在一個(gè)賬戶被其他的業(yè)務(wù)鎖定則無法完成轉(zhuǎn)賬業(yè)務(wù)
        return false;
      }else {
        als.add(from);
        als.add(to);
      }
      return true;
    }
    //歸還資源
    synchronized void free(Object from,Object to){
      als.remove(from);
      als.remove(to);
    }
  }
  class Account {
    //actr應(yīng)該為單例
    private Allocator actr;
    private int balance;
    //轉(zhuǎn)賬
    void transfer(Account target, int amt){
      //一次性申請(qǐng)轉(zhuǎn)出和轉(zhuǎn)入賬戶，直到成功
      while (!actr.apply(this,target));
      try{
        //鎖定轉(zhuǎn)出賬戶
        synchronized (this){
          //鎖定轉(zhuǎn)入賬戶
          synchronized (target){
            if (this.balance > amt){
              this.balance -= amt;
              target.balance += amt;
            }
          }
        }
      }finally {
        actr.free(this, target);
      }
    }
  }

class Accounts{
    private int id;
    private int balance;
    //轉(zhuǎn)賬
    void transfer(Accounts target,int amt){
      Accounts left = this;
      Accounts right = target;
      if (this.id > target.id){
        left = target;
        right = this;
      }
      //鎖定序號(hào)小的賬戶
      synchronized (left){
        //鎖定序號(hào)大的賬戶
        synchronized (right){
          if (this.balance > amt){
            this.balance -= amt;
            target.balance += amt;
          }
        }
      }
    }
  }