我将把这个留给更多的访问者，因为对我来说，这是关于主线程无法System.out.println的一些事情。

public class LogUtil {

private static String log = "";
private static boolean started = false;
public static void print(String s) {
    //Start the thread unless it's already running
    if(!started) {
        start();
    }
    //Append a String to the log
    log += s;
}

public static void println(String s) {
    //Start the thread unless it's already running
    if(!started) {
        start();
    }
    //Append a String to the log with a newline.
    //NOTE: Change to print(s + "\n") if you don't want it to trim the last newline.
    log += (s.endsWith("\n") )? s : (s + "\n");
}

private static void start() {
    //Creates a new Thread responsible for showing the logs.
    Thread thread = new Thread(new Runnable() {
        @Override
        public void run() {
            while(true) {
                //Execute 100 times per second to save CPU cycles.
                try {
                    Thread.sleep(10);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                //If the log variable has any contents...
                if(!log.isEmpty()) {
                    //...print it and clear the log variable for new data.
                    System.out.print(log);
                    log = "";
                }
            }
        }
    });
    thread.start();
    started = true;
}
}

用法:LogUtil。println("这是一个字符串");

使用Log类。输出与LogCat可见

是的。如果您正在使用模拟器，它将显示在系统下的Logcat视图中。标签。编写一些东西并在模拟器中进行尝试。

当然，要在logcat中看到结果，您应该至少将日志级别设置为“Info”(logcat中的日志级别);否则，就像我遇到的那样，您将看不到您的输出。

我将把这个留给更多的访问者，因为对我来说，这是关于主线程无法System.out.println的一些事情。

public class LogUtil {

private static String log = "";
private static boolean started = false;
public static void print(String s) {
    //Start the thread unless it's already running
    if(!started) {
        start();
    }
    //Append a String to the log
    log += s;
}

public static void println(String s) {
    //Start the thread unless it's already running
    if(!started) {
        start();
    }
    //Append a String to the log with a newline.
    //NOTE: Change to print(s + "\n") if you don't want it to trim the last newline.
    log += (s.endsWith("\n") )? s : (s + "\n");
}

private static void start() {
    //Creates a new Thread responsible for showing the logs.
    Thread thread = new Thread(new Runnable() {
        @Override
        public void run() {
            while(true) {
                //Execute 100 times per second to save CPU cycles.
                try {
                    Thread.sleep(10);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                //If the log variable has any contents...
                if(!log.isEmpty()) {
                    //...print it and clear the log variable for new data.
                    System.out.print(log);
                    log = "";
                }
            }
        }
    });
    thread.start();
    started = true;
}
}

用法:LogUtil。println("这是一个字符串");

Correction: On the emulator and most devices System.out.println gets redirected to LogCat and printed using Log.i(). This may not be true on very old or custom Android versions. Original: There is no console to send the messages to so the System.out.println messages get lost. In the same way this happens when you run a "traditional" Java application with javaw. Instead, you can use the Android Log class: Log.d("MyApp","I am here"); You can then view the log either in the Logcat view in Eclipse, or by running the following command: adb logcat It's good to get in to the habit of looking at logcat output as that is also where the Stack Traces of any uncaught Exceptions are displayed. The first Entry to every logging call is the log tag which identifies the source of the log message. This is helpful as you can filter the output of the log to show just your messages. To make sure that you're consistent with your log tag it's probably best to define it once as a static final String somewhere. Log.d(MyActivity.LOG_TAG,"Application started"); There are five one-letter methods in Log corresponding to the following levels: e() - Error w() - Warning i() - Information d() - Debug v() - Verbose wtf() - What a Terrible Failure The documentation says the following about the levels: Verbose should never be compiled into an application except during development. Debug logs are compiled in but stripped at runtime. Error, warning and info logs are always kept.