Java printf() 和 println() 的区别是什么？

Question

1.在学习Java7 concurrency cookbook 的第一章节时，发现《Interrupting a thread》这个部分的代码没有达到预期的效果：控制台并没有像书上所描述的那样输出内容。再把其使用的printf()函数换成println()之后；程序得到预期的效果。
2.代码如下：

package lee.twowater.java7.chapterThree;

public class PrimeGenerator extends Thread {

    @Override
    public void run() {
        long number = 1L;
        while (true) {
            if (isPrime(number)) {
                System.out.printf("Number "+ number +" is Prime");
            }
            
            if (isInterrupted()) {
                System.out.printf("The Prime Generator has been Interrupted");
                return;
            }
            number++;
        }
    }
    
    private boolean isPrime(long number) {
        if (number <= 2) {
            return true;
        }
        for (long i = 2; i < number; i++) {
            if ((number % i) == 0) {
                return false;
            }
        }
        return true;
    }
}

    package lee.twowater.java7.chapterThree;

public class Main {
    public static void main(String[] args) {
        Thread task = new PrimeGenerator();
        task.start();
        
        try {
            Thread.sleep(5000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        
        task.interrupt();
    }
}

3.我猜想println()和printf()除了换行和格式化的差异之外，是不是在缓存方面还存在差异？

Answer 1

It seems to have nothing to do with caching. The source code of println is like this:

public void println(String x) {
        synchronized (this) {
            print(x);
            newLine();
        }
    }

Then the source code of printf:

    public PrintStream printf(String format, Object ... args) {
        return format(format, args);
    }

In format, there is nothing more than simple formatting operations

    public PrintStream format(String format, Object ... args) {
        try {
            synchronized (this) {
                ensureOpen();
                if ((formatter == null)
                    || (formatter.locale() != Locale.getDefault()))
                    formatter = new Formatter((Appendable) this);
                formatter.format(Locale.getDefault(), format, args);
            }
        } catch (InterruptedIOException x) {
            Thread.currentThread().interrupt();
        } catch (IOException x) {
            trouble = true;
        }
        return this;
    }

As for your question, you can change the sentence printed in the code to:

                System.out.printf("Number is Prime: %d", number);
                System.out.print("\r");

That’s it

Answer 2

Perhaps if you encounter problems, you can use Baidu first. .
http://www.jb51.net/article/4...

Answer 3

Integer number = 55;
System.out.printf("Number " + number + " is Prime\n");
System.out.printf("Number %s is Prime", number);

Newline is a difference, but the main difference is that printfexpressions can be formatted. For specific format syntax, please refer to java.util.Formatter