Question

我希望以下代码能够在设置静态变量值的语句之前打印行，但是它没有按预期工作。

import java.io.PrintWriter;
class Bank{
private static boolean isInCrisis = false;
public static boolean getIsInCrisis(){return Bank.isInCrisis;}
public static boolean setIsInCrisis(boolean crisis){
    return Bank.isInCrisis = crisis; 
}
public String getCash() throws Exception{
    if(!Bank.isInCrisis){
        return new String("$100"); 
    }
    else{
        throw new Exception("Bank is in crisis"); 
    }
}
}

public class InstanceObjects{
public static void main(String... st) {
    try{
        Bank hsbc = new Bank();
        PrintWriter writer = new PrintWriter(System.out);
        writer.printf("collect cash: %s\n",hsbc.getCash());
        writer.printf("collect cash: %s\n",hsbc.getCash());
        writer.printf("collect cash: %s\n",hsbc.getCash());
        writer.printf("collect cash: %s\n",hsbc.getCash());
        writer.printf("collect cash: %s\n",hsbc.getCash());
        writer.printf("collect cash: %s\n",hsbc.getCash());
        writer.printf("collect cash: %s\n",hsbc.getCash());
        hsbc.setIsInCrisis(true);
        writer.printf("collect cash: %s\n",hsbc.getCash());            
        writer.close(); 
    }catch(Exception e){
        e.printStackTrace(); 
    }
}
}

输出抛出异常“银行处于危机中”，但它应首先打印一些“收取现金...”消息然后抛出异常消息......

Answer 1

问题是你的PrintWriter永远不会被刷新。它正在累积数据，但它永远不会将其写入控制台，因为在缓冲区已满之前会抛出异常。

如果您在引发异常的来电之前致电writer.flush()，则会看到预期的消息。

如果您在finally块中关闭作者，则会在数据关闭时看到数据，因为这也会使作者刷新...但在异常之后，如catch在finally之前执行。

如果您使用try-with-resources块，则会在异常之前看到数据，因为close发生在＆＃34;嵌套＆＃34;尝试/终于，有效：

try (PrintWriter writer = new PrintWriter(System.out)) { Bank hsbc = new Bank(); ... } catch(Exception e){ // writer will already be closed here e.printStackTrace(); }

Answer 2

你忘记了

writer.flush();

printf方法不会自动刷新，您的消息位于永远不会发送到控制台的缓冲区中。

Answer 3

在获取抛出异常的消息之前，请尝试刷新流。

public class Main{ public static void main(String... st) {
    try{
        Bank hsbc = new Bank();
        PrintWriter writer = new PrintWriter(System.out);
        writer.printf("collect cash: %s\n",hsbc.getCash());
        writer.printf("collect cash: %s\n",hsbc.getCash());
        writer.printf("collect cash: %s\n",hsbc.getCash());
        writer.printf("collect cash: %s\n",hsbc.getCash());
        writer.printf("collect cash: %s\n",hsbc.getCash());
        writer.printf("collect cash: %s\n",hsbc.getCash());
        writer.printf("collect cash: %s\n",hsbc.getCash());
        writer.flush();
        hsbc.setIsInCrisis(true);
        writer.printf("collect cash: %s\n",hsbc.getCash());            
        writer.close(); 
    }catch(Exception e){
        e.printStackTrace(); 
    } } }

打印：

collect cash: $100
collect cash: $100
collect cash: $100
collect cash: $100
collect cash: $100
collect cash: $100
collect cash: $100
java.lang.Exception: Bank is in crisis
    at Bank.getCash(Main.java:13)
    at Main.main(Main.java:32)

java字节码是不是按顺序执行？

3 个答案: