在Java中，如何将左填充的零添加到数字？

Question

我有一个整数100，我如何格式化它看起来像00000100 (总是8位数长度)？

Answer 1

试试这个：

String formattedNumber = String.format("%08d", number);

Answer 2

您还可以使用类DecimalFormat，如下所示：

NumberFormat formatter = new DecimalFormat("00000000");
System.out.println(formatter.format(100)); // 00000100

Answer 3

还有另一种方式。;)

int x = ...
String text = (""+(500000000 + x)).substring(1);

-1 \f25 => 99999999 -1\f6(9补码)

import java.util.concurrent.Callable;
/* Prints.
String.format("%08d"): Time per call 3822
(""+(500000000+x)).substring(1): Time per call 593
Space holder: Time per call 730
 */
public class StringTimer {
    public static void time(String description, Callable<String> test) {
        try {
            // warmup
            for(int i=0;i<10*1000;i++)
                test.call();
            long start = System.nanoTime();
            for(int i=0;i<100*1000;i++)
                test.call();
            long time = System.nanoTime() - start;
            System.out.printf("%s: Time per call %d%n", description, time/100/1000);
        } catch (Exception e) {
            System.out.println(description+" failed");
            e.printStackTrace();
        }
    }

    public static void main(String... args) {
        time("String.format(\"%08d\")", new Callable<String>() {
            int i =0;
            public String call() throws Exception {
                return String.format("%08d", i++);
            }
        });
        time("(\"\"+(500000000+x)).substring(1)", new Callable<String>() {
            int i =0;
            public String call() throws Exception {
                return (""+(500000000+(i++))).substring(1);
            }
        });
        time("Space holder", new Callable<String>() {
            int i =0;
            public String call() throws Exception {
                String spaceHolder = "00000000";
                String intString = String.valueOf(i++);
                return spaceHolder.substring(intString.length()).concat(intString);
            }
        });
    }
}