“你好，阿米戈！今天，你将学习如何执行一项新任务：替换 System.out 对象。”
System.out 是 System 类中名为 out 的 static PrintStream 变量。此变量包含 final 修饰符，因此你可以直接为其赋予新值。但是，System 类包含一个可以执行此操作的特殊方法：setOut(PrintStream stream)。这就是我们将要使用的方法。
“真有趣。我们用什么替换它？”
“我们需要一些可以收集输出数据的对象。ByteArrayOutputStream 最适合此项工作。这是一个特殊的类，它是一个动态（可调整大小的）数组，并实现 OutputStream 接口。”
“数组和 OutputStream 之间的适配器？”
“差不多。代码看起来如下所示。”
代码
public static void main(String[] args) throws Exception
{
//Save the current PrintStream in a special variable
PrintStream consoleStream = System.out;
//Create a dynamic array
ByteArrayOutputStream outputStream = new ByteArrayOutputStream();
//Create an adapter for the PrintStream class
PrintStream stream = new PrintStream(outputStream);
//Set it as the current System.out
System.setOut(stream);
//Call a function that knows nothing about our changes
printSomething();
//Convert the data written to our ByteArray into a string
String result = outputStream.toString();
//Put everything back to the way it was
System.setOut(consoleStream);
}
public static void printSomething()
{
System.out.println("Hi");
System.out.println("My name is Amigo");
System.out.println("Bye-bye!");
}
“我们将如何处理此行？”
“嗯，怎么处理都行。例如，可以将其反转。则代码如下所示：”
代码
public static void main(String[] args) throws Exception
{
//Save the current PrintStream in a special variable
PrintStream consoleStream = System.out;
//Create a dynamic array
ByteArrayOutputStream outputStream = new ByteArrayOutputStream();
//Create an adapter for the PrintStream class
PrintStream stream = new PrintStream(outputStream);
//Set it as the current System.out
System.setOut(stream);
//Call a function that knows nothing about our changes
printSomething();
//Convert the data written to our ByteArray into a string
String result = outputStream.toString();
//Put everything back to the way it was
System.setOut(consoleStream);
//Reverse the string
StringBuilder stringBuilder = new StringBuilder(result);
stringBuilder.reverse();
String reverseString = stringBuilder.toString();
//Output it to the console
System.out.println(reverseString);
}
public static void printSomething()
{
System.out.println("Hi");
System.out.println("My name is Amigo");
System.out.println("Bye-bye!");
}“太有趣了！现在，我开始对这些小型类提供的强大功能有所了解了。”
“比拉博，谢谢你给我上了有趣的一课。”
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