Java Printf 函数及其使用
2015-08-01 11:22
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Java Printf 函数及其使用
System.out.printf() 是在JDK1.5版引入的方法，printf 方法有 printf(String format, Object ... args) 和 printf(Locale l, String format, Object ... args) 两种重载方式。printf 方法的代码解析
printf(String format, Object ... args) 方法的代码/**
* A convenience method to write a formatted string to this output stream
* using the specified format string and arguments.
*
* <p> An invocation of this method of the form <tt>out.printf(format,
* args)</tt> behaves in exactly the same way as the invocation
*
* <pre>
* out.format(format, args) </pre>
*
* @param format
* A format string as described in <a
* href="../util/Formatter.html#syntax">Format string syntax</a>
* * @param args
* Arguments referenced by the format specifiers in the format
* string. If there are more arguments than format specifiers, the
* extra arguments are ignored. The number of arguments is
* variable and may be zero. The maximum number of arguments is
* limited by the maximum dimension of a Java array as defined by
* <cite>The Java™ Virtual Machine Specification</cite>.
* The behaviour on a
* <tt>null</tt> argument depends on the <a
* href="../util/Formatter.html#syntax">conversion</a>.
* * @throws java.util.IllegalFormatException
* If a format string contains an illegal syntax, a format
* specifier that is incompatible with the given arguments,
* insufficient arguments given the format string, or other
* illegal conditions. For specification of all possible
* formatting errors, see the <a
* href="../util/Formatter.html#detail">Details</a> section of the
* formatter class specification.
*
* @throws NullPointerException
* If the <tt>format</tt> is <tt>null</tt>
*
* @return This output stream
*
* @since 1.5
*/
public PrintStream printf(String format, Object ... args) {
return format(format, args);
}public PrintStream format(String format, Object ... args) {
try {
synchronized (this) {
ensureOpen();
if ((formatter == null)
|| (formatter.locale() != Locale.getDefault()))
formatter = new Formatter((Appendable) this);
<span style="background-color: rgb(51, 255, 51);">formatter.format(Locale.getDefault(), format, args);</span>
}
} catch (InterruptedIOException x) {
Thread.currentThread().interrupt();
} catch (IOException x) {
trouble = true;
}
return this;
} printf(Locale l, String format, Object ... args) 方法的代码 /** * A convenience method to write a formatted string to this output stream * using the specified format string and arguments. * * <p> An invocation of this method of the form <tt>out.printf(l, format, * args)</tt> behaves in exactly the same way as the invocation * * <pre> * out.format(l, format, args) </pre> * * @param l * The <a target=_blank href="mailto:{@linkplain">{@linkplain</a> java.util.Locale locale} to apply during * formatting. If <tt>l</tt> is <tt>null</tt> then no localization * is applied. * * @param format * A format string as described in <a * href="../util/Formatter.html#syntax">Format string syntax</a> * * @param args * Arguments referenced by the format specifiers in the format * string. If there are more arguments than format specifiers, the * extra arguments are ignored. The number of arguments is * variable and may be zero. The maximum number of arguments is * limited by the maximum dimension of a Java array as defined by * <cite>The Java™ Virtual Machine Specification</cite>. * The behaviour on a * <tt>null</tt> argument depends on the <a * href="../util/Formatter.html#syntax">conversion</a>. * * @throws java.util.IllegalFormatException * If a format string contains an illegal syntax, a format * specifier that is incompatible with the given arguments, * insufficient arguments given the format string, or other * illegal conditions. For specification of all possible * formatting errors, see the <a * href="../util/Formatter.html#detail">Details</a> section of the * formatter class specification. * * @throws NullPointerException * If the <tt>format</tt> is <tt>null</tt> * * @return This output stream * * @since 1.5 */ public PrintStream printf(Locale l, String format, Object ... args) { return format(l, format, args); } public PrintStream format(Locale l, String format, Object ... args) { try { synchronized (this) { ensureOpen(); if ((formatter == null) || (formatter.locale() != l)) formatter = new Formatter(this, l); <span style="background-color: rgb(51, 255, 51);">formatter.format(l, format, args);</span> } } catch (InterruptedIOException x) { Thread.currentThread().interrupt(); } catch (IOException x) { trouble = true; } return this; } 从以上的两个重载代码可以看出，printf(String format, Object ... args) 就是基于Java环境的打印格式化方法实现，printf(Locale l, String format, Object ... args) 只是多了指定环境的适应的打印操作。printf 方法的使用
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package cn.lwz.javase.test; import java.math.BigDecimal; import java.math.BigInteger; import org.junit.Test; /** * Printf 方法测试类 * @author LiWenZhang * @date 2015-08-01 */ public class TestPrintf {@Testpublic void testPrintf() throws Exception {printBool();printHash();printStr();printChar();printInt();printOct();printHex();printExp();printFlo();}/*** 'f' 浮点 结果被格式化为十进制浮点数，可用于float、double、Float、Double、BigDecimal*/private void printFlo() {printf(getFormat("f"), 100000000f, 200000000d, 300000000F, 400000000D, BigDecimal.valueOf(0x7fffffffffffffffL));}/*** 'e', 'E' 浮点 结果被格式化为用计算机科学记数法表示的十进制数。* 可用于float、double、Float、Double、BigDecimal，‘%e’表示字母输出以小写表示，‘%E’则表示以大写表示*/private void printExp() {printf(getFormat("e") + ", " + getFormat("E"), 100000000f, 200000000d, 300000000F, 400000000D,BigDecimal.valueOf(0x7fffffffffffffffL));}/*** 'x', 'X' 整数 结果被格式化为十六进制整数。* 可用于byte、short、int、long、Byte、Short、Integer、Long、BigInteger，* ‘%x’表示字母输出以小写表示，‘%X’则表示以大写表示*/private void printHex() {printf(getFormat("x") + ", " + getFormat("X"), (byte) 100, (short) 200, 0,BigInteger.valueOf(0x7fffffffffffffffL));}/*** 'o' 整数* 结果被格式化为八进制整数，可用于byte、short、int、long、Byte、Short、Integer、Long、BigInteger*/private void printOct() {printf(getFormat("o"), (byte) 100, (short) 200, 0, BigInteger.valueOf(0x7fffffffffffffffL));}/*** 'b', 'B' 常规 如果参数 arg 为 null，则结果为 "false"。 如果 arg 是一个 boolean 值或* Boolean，则结果为String.valueOf() 返回的字符串。否则结果为 "true"。*/private void printBool() {printf(getFormat("b") + ", " + getFormat("B"), true, false, "true", "false", 0, 'A');}/*** 'h', 'H' 常规 如果参数 arg 为 null，则结果为 "null"。 否则，结果为调用* Integer.toHexString(arg.hashCode()) 得到的结果。*/private void printHash() {printf(getFormat("h") + ", " + getFormat("H"), true, false, "true", 0, 'A');}/*** 's', 'S' 常规 如果参数 arg 为 null，则结果为 "null"。 如果 arg 实现 Formattable，则调用* arg.formatTo。否则，结果为调用arg.toString() 得到的结果。*/private void printStr() {printf(getFormat("s") + ", " + getFormat("S"), true, false, "true", 0, 'A');}/*** 'c', 'C' 字符 结果是一个 Unicode 字符。* 可用于byte、short、char、Byte、Short、Character、Integer，* ‘%c’表示字母输出以小写表示，‘%C’则表示以大写表示*/private void printChar() {printf(getFormat("c") + ", " + getFormat("C"), (byte) 65, 97, 'A');}/*** 'd' 整数* 结果被格式化为十进制整数，可用于byte、short、int、long、Byte、Short、Integer、Long、BigInteger*/private void printInt() {printf(getFormat("d"), (byte) 65, 97, BigInteger.valueOf(0x7fffffffffffffffL));}private void printf(String formatStr, Object... args) {Util.printMethodName();if (args != null && args.length > 0) {for (Object arg : args) {System.out.printf("param：" + arg + Util.getBlanks(arg, 25));System.out.printf(formatStr + "\n", arg, arg);}}}private String getFormat(String f) {return "Format: %%" + f + " >> %" + f;} }结果输出：
---------------------------------- printBool() ----------------------------------param：true Format: %b >> true, Format: %B >> TRUEparam：false Format: %b >> false, Format: %B >> FALSEparam：true Format: %b >> true, Format: %B >> TRUEparam：false Format: %b >> true, Format: %B >> TRUEparam：0 Format: %b >> true, Format: %B >> TRUEparam：A Format: %b >> true, Format: %B >> TRUE
---------------------------------- printHash() ----------------------------------param：true Format: %h >> 4cf, Format: %H >> 4CFparam：false Format: %h >> 4d5, Format: %H >> 4D5param：true Format: %h >> 36758e, Format: %H >> 36758Eparam：0 Format: %h >> 0, Format: %H >> 0param：A Format: %h >> 41, Format: %H >> 41
---------------------------------- printStr() ----------------------------------param：true Format: %s >> true, Format: %S >> TRUEparam：false Format: %s >> false, Format: %S >> FALSEparam：true Format: %s >> true, Format: %S >> TRUEparam：0 Format: %s >> 0, Format: %S >> 0param：A Format: %s >> A, Format: %S >> A
---------------------------------- printChar() ----------------------------------param：65 Format: %c >> A, Format: %C >> Aparam：97 Format: %c >> a, Format: %C >> Aparam：A Format: %c >> A, Format: %C >> A
---------------------------------- printInt() ----------------------------------param：65 Format: %d >> 65param：97 Format: %d >> 97param：9223372036854775807 Format: %d >> 9223372036854775807
---------------------------------- printOct() ----------------------------------param：100 Format: %o >> 144param：200 Format: %o >> 310param：0 Format: %o >> 0param：9223372036854775807 Format: %o >> 777777777777777777777
---------------------------------- printHex() ----------------------------------param：100 Format: %x >> 64, Format: %X >> 64param：200 Format: %x >> c8, Format: %X >> C8param：0 Format: %x >> 0, Format: %X >> 0param：9223372036854775807 Format: %x >> 7fffffffffffffff, Format: %X >> 7FFFFFFFFFFFFFFF
---------------------------------- printExp() ----------------------------------param：1.0E8 Format: %e >> 1.000000e+08, Format: %E >> 1.000000E+08param：2.0E8 Format: %e >> 2.000000e+08, Format: %E >> 2.000000E+08param：3.0E8 Format: %e >> 3.000000e+08, Format: %E >> 3.000000E+08param：4.0E8 Format: %e >> 4.000000e+08, Format: %E >> 4.000000E+08param：9223372036854775807 Format: %e >> 9.223372e+18, Format: %E >> 9.223372E+18
---------------------------------- printFlo() ----------------------------------param：1.0E8 Format: %f >> 100000000.000000param：2.0E8 Format: %f >> 200000000.000000param：3.0E8 Format: %f >> 300000000.000000param：4.0E8 Format: %f >> 400000000.000000param：9223372036854775807 Format: %f >> 9223372036854775807.000000
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