printf<\/code> method to write a formatted string to the PrintStream<\/code> object since version 5. Here are the method’s signatures:<\/p>\npublic PrintStream printf(Locale l, String format, Object... args)\npublic PrintStream printf(String format, Object... args)<\/pre>\n
\nl<\/code> – a locale<\/a> to apply during formatting<\/li>\nformat<\/code> – a format string as described in format string syntax<\/a><\/li>\nargs<\/code> – arguments referenced by the format specifiers in the format<\/code> string<\/li>\n<\/ul>\n You can also check this tutorial in the following video: <\/p>\n
\n![\"\"](\"https:\/\/examples.javacodegeeks.com\/wp-content\/uploads\/2022\/07\/Printf-Java-Example-1024x576.jpg\")
<\/a>Printf Java Example – Video<\/figcaption><\/figure>\n<\/div>\nThe printf method can format a string which contains formatting specifiers for Integer<\/code>, float<\/code>, Date<\/code>, String<\/code>, etc. The formatting specifiers start with %<\/code> and is followed by four optional arguments and one mandatory conversion<\/code> argument.<\/p>\n%[argument_index$][flags][width][.precision]conversion<\/pre>\n\n![\"system.out.printf\"](\"http:\/\/examples.javacodegeeks.com\/wp-content\/uploads\/2012\/12\/java-logo.jpg\")
<\/figure>\n<\/div>\n\nargument_index<\/code> – it is an optional decimal integer indicating the position of the argument in the argument list. The first argument is referenced by “1$”, the second by “2$”, etc.<\/li>\nflags<\/code> – it is an optional set of characters that modify the output format. The set of valid flags depends on the conversion.<\/li>\nwidth<\/code> – it is an optional positive decimal integer indicating the minimum number of characters to be written to the output.<\/li>\nprecision<\/code> – it is an optional non-negative decimal integer used to restrict the number of characters.<\/li>\nconversion<\/code> – it is a mandatory character indicating how the argument should be formatted.<\/li>\n<\/ul>\nIn this example, I will demonstrate how to format a string with these formatting specifiers.<\/p>\n
2. Technologies Used<\/h2>\n
The example code in this example was built and run with:<\/p>\n
\n- Java 11<\/li>\n
- Maven 3.3<\/li>\n
- Eclipse<\/li>\n
- Junit 4.12<\/li>\n<\/ul>\n
3. Maven Project<\/h2>\n3.1 Dependencies<\/h3>\n
I will include Junit<\/code> in the pom.xml<\/code>.<\/p>\npom.xml<\/em><\/span>\n<\/p>\n<project xmlns=\"http:\/\/maven.apache.org\/POM\/4.0.0\"\n\txmlns:xsi=\"http:\/\/www.w3.org\/2001\/XMLSchema-instance\"\n\txsi:schemaLocation=\"http:\/\/maven.apache.org\/POM\/4.0.0 http:\/\/maven.apache.org\/xsd\/maven-4.0.0.xsd\">\n\t<modelVersion>4.0.0<\/modelVersion>\n\t<groupId>java-printf-demo<\/groupId>\n\t<artifactId>java-printf-demo<\/artifactId>\n\t<version>0.0.1-SNAPSHOT<\/version>\n\t<build>\n\t\t<sourceDirectory>src<\/sourceDirectory>\n\t\t<plugins>\n\t\t\t<plugin>\n\t\t\t\t<artifactId>maven-compiler-plugin<\/artifactId>\n\t\t\t\t<version>3.8.0<\/version>\n\t\t\t\t<configuration>\n\t\t\t\t\t<release>11<\/release>\n\t\t\t\t<\/configuration>\n\t\t\t<\/plugin>\n\t\t<\/plugins>\n\t<\/build>\n\t<dependencies>\n\t\t<dependency>\n\t\t\t<groupId>junit<\/groupId>\n\t\t\t<artifactId>junit<\/artifactId>\n\t\t\t<version>4.12<\/version>\n\t\t<\/dependency>\n\t<\/dependencies>\n<\/project><\/pre>\n3.2 PrintfFormatBaseTest<\/h3>\n
Java Formatter<\/a> class defines the formatting specifiers. Here are some common conversion specifiers:<\/p>\n\n- b(B) – converts a non-null
boolean<\/code> or Boolean<\/code> object base on String.valueOf(arg)<\/code>.<\/li>\n- c(C) – transforms a character based on its Unicode<\/li>\n
- h – translates based on the
hashcode<\/code> method<\/li>\n- d – converts an integer number<\/li>\n
- f – converts a float number<\/li>\n
- n – converts to a platform-specific line separator <\/li>\n
- s(S) – formats a String<\/li>\n
- t(T) – converts to a date and time value<\/li>\n<\/ul>\n
The following are some common flag specifiers:<\/p>\n
\n- -: Left-justified<\/li>\n
- +: Include a sign for a numeric value<\/li>\n
- 0: Zero-padding for a numeric value<\/li>\n
- ,: locale-specific grouping separators <\/li>\n<\/ul>\n
In this example, I will create several constants which embed the format specifiers. I will use Junit @Rule<\/code> to print out the test method’s name. I will also create several test methods to demonstrate the three kinds of argument indexing:<\/p>\n\n- explicit indexing – specifies the argument with explicit indexing, e.g.
1$<\/code><\/li>\n- ordinary indexing – the argument-index is based on the position<\/li>\n
- relative indexing – uses the same argument with
'<'<\/code><\/li>\n<\/ul>\nIn the test methods I use the System.out.printf method.<\/p>\n
PrintfFormatBaseTest.java<\/em><\/span> <\/p>\npackage jcg.zheng.demo;\n\nimport java.util.MissingFormatArgumentException;\n\nimport org.junit.Rule;\nimport org.junit.Test;\nimport org.junit.rules.TestRule;\nimport org.junit.rules.TestWatcher;\nimport org.junit.runner.Description;\n\npublic class PrintfFormatBaseTest {\n\t\n\t@Rule\n\tpublic TestRule echoMethodName = new TestWatcher() {\n\t\tprotected void starting(Description desc) {\n\t\t\tSystem.out.println(\"\\nTestMethodName:\" + desc.getMethodName());\n\t\t}\n\t};\n \n\tprotected static final String BOOLEAN_B = \"%%b - format boolean value: %b, %%B - Boolean value: %B\";\n\tprotected static final String CHAR_C = \"%%c - format char with lower-case value: %c, %%C - with upper-case value: %C.\";\n\tprotected static final String DECIMAL_F = \"%%f - doubleValue is: %f. floatValue is: %f\";\n\tprotected static final String DECIMAL_FLAGS_WIDTH_PRECISION = \"%%-+,10.2f - Format a negative number by left-justified, separating with comma, with a sign, 10 width, and 2 precision: %-+,10.2f\";\n\tprotected static final String DECIMAL_PADDING_BLANK = \"%% 10.3f - Format a decimal with padding empty space: % 10.3f\";\n\tprotected static final String DECIMAL_PADDING_ZERO = \"%%010.3f - Format a decimal with padding zero: %010.3f\";\n\n\tprotected static final String EXPONENTIAL_E = \"%%e - exponential number. Value is: %e.\";\n\n\tprotected static final String HASHCODE_H = \"The string object's hashcode: %h, the interger's hashcode: %h\";\n\tprotected static final String INTEGER_D_BASE10 = \"%%d - byteValue is: %d, shortValue is: %d, intValue is: %d, longValue is: %d.\";\n\n\tprotected static final String INTEGER_O_BASE8 = \"%%o - Octal format. byteValue is: %o, shortValue is: %o, intValue is: %o, longValue is: %o.\";\n\tprotected static final String INTEGER_X_BASE16 = \"%%x - Base 16. byteValue is: %x, shortValue is: %x, intValue is: %x, longValue is: %x.\";\n\tprotected static final String NEW_LINE = \"%n\";\n\n\tprotected byte byteValue = 12;\n\tprotected double doubleValue = 10.123;\n\tprotected float floatValue = 123.45f;\n\tprotected int intValue = 123;\n\tprotected long longValue = 1234567;\n\tprotected short shortValue = 121;\n\n\t@Test\n\tpublic void explicit_indexing_test() {\n\t\tSystem.out.printf(\"explicit two arguments: %1$s, %2$s\", \"Hello\", \"World!\");\t\t \n\t}\n\n\t@Test\n\tpublic void explicit_indexing_test_differentOrder() {\n\t\tSystem.out.printf(\"explicit two arguments: %2$s, %1$s\", \"Hao!\", \"Ni\");\t \n\t}\n\n\t@Test(expected = MissingFormatArgumentException.class)\n\tpublic void ordinary_indexing_test_exception() {\n\t\tSystem.out.printf(\"throw MissingFormatArgumentException: %s, %s\", \"test\");\t \n\t}\n\n\t@Test\n\tpublic void relative_indexing_test() {\n\t\tSystem.out.printf(\"relative arguments - %1$s, %<s, %<s, %2$s, and %<s\", \"Zheng\", \"Mary\");\t \n\t}\n\t\n}<\/pre>\nExecute mvn test -Dtest=PrintfFormatBaseTest<\/code> and capture the output.<\/p>\nPrintfFormatBaseTest results.<\/em><\/span>\n<\/p>\nC:\\MaryZheng\\Workspaces\\jdk12\\java-printf-demo>mvn test -Dtest=PrintfFormatBaseTest\n[INFO] Scanning for projects...\n[INFO]\n[INFO] -----------------< java-printf-demo:java-printf-demo >------------------\n[INFO] Building java-printf-demo 0.0.1-SNAPSHOT\n[INFO] --------------------------------[ jar ]---------------------------------\n[INFO]\n[INFO] --- maven-resources-plugin:2.6:resources (default-resources) @ java-printf-demo ---\n[WARNING] Using platform encoding (Cp1252 actually) to copy filtered resources, i.e. build is platform dependent!\n[INFO] skip non existing resourceDirectory C:\\MaryZheng\\Workspaces\\jdk12\\java-printf-demo\\src\\main\\resources\n[INFO]\n[INFO] --- maven-compiler-plugin:3.8.0:compile (default-compile) @ java-printf-demo ---\n[INFO] Changes detected - recompiling the module!\n[WARNING] File encoding has not been set, using platform encoding Cp1252, i.e. build is platform dependent!\n[INFO] Compiling 7 source files to C:\\MaryZheng\\Workspaces\\jdk12\\java-printf-demo\\target\\classes\n[INFO]\n[INFO] --- maven-resources-plugin:2.6:testResources (default-testResources) @ java-printf-demo ---\n[WARNING] Using platform encoding (Cp1252 actually) to copy filtered resources, i.e. build is platform dependent!\n[INFO] skip non existing resourceDirectory C:\\MaryZheng\\Workspaces\\jdk12\\java-printf-demo\\src\\test\\resources\n[INFO]\n[INFO] --- maven-compiler-plugin:3.8.0:testCompile (default-testCompile) @ java-printf-demo ---\n[INFO] Changes detected - recompiling the module!\n[WARNING] File encoding has not been set, using platform encoding Cp1252, i.e. build is platform dependent!\n[INFO] Compiling 7 source files to C:\\MaryZheng\\Workspaces\\jdk12\\java-printf-demo\\target\\test-classes\n[INFO]\n[INFO] --- maven-surefire-plugin:2.12.4:test (default-test) @ java-printf-demo ---\n[INFO] Surefire report directory: C:\\MaryZheng\\Workspaces\\jdk12\\java-printf-demo\\target\\surefire-reports\n\n-------------------------------------------------------\n T E S T S\n-------------------------------------------------------\nRunning jcg.zheng.demo.PrintfFormatBaseTest\n\nTestMethodName:explicit_indexing_test_differentOrder\nexplicit two arguments: Ni, Hao!\nTestMethodName:relative_indexing_test\nrelative arguments - Zheng, Zheng, Zheng, Mary, and Mary\nTestMethodName:explicit_indexing_test\nexplicit two arguments: Hello, World!\nTestMethodName:ordinary_indexing_test_exception\nthrow MissingFormatArgumentException: test, Tests run: 4, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 0.157 sec\n\nResults :\n\nTests run: 4, Failures: 0, Errors: 0, Skipped: 0\n\n[INFO] ------------------------------------------------------------------------\n[INFO] BUILD SUCCESS\n[INFO] ------------------------------------------------------------------------\n[INFO] Total time: 10.262 s\n[INFO] Finished at: 2019-07-07T11:50:17-05:00\n[INFO] ------------------------------------------------------------------------\n\nC:\\MaryZheng\\Workspaces\\jdk12\\java-printf-demo><\/pre>\n4. Format a Number<\/h2>\n4.1 Printf_NumberTest<\/h3>\n
In this step, I will create Junit tests to format a number in several ways:
<\/div> <\/div><\/p>\n\n- Formats a number (base 8, 10, and 16) for different data types:
byte<\/code>, short<\/code>, int<\/code>, and long<\/code><\/li>\n- Formats a float number in exponential format<\/li>\n
- Formats a decimal number for different data types:
float<\/code> and double<\/code><\/li>\n- Formats a decimal number with different padding characters: space and zero<\/li>\n
- Formats a float number with left-justified (-), sign (+), and comma (,) flag, 2 precision (.2), and width 10 specifiers<\/li>\n<\/ul>\n
In the test methods I use the System.out.printf method. <\/p>\n
Printf_NumberTest.java<\/em><\/span> <\/p>\npackage jcg.zheng.demo;\n\nimport org.junit.Test;\n\npublic class Printf_NumberTest extends PrintfFormatBaseTest {\n\n\n\t@Test\n\tpublic void d_for_integer_base10() {\n\t\tSystem.out.printf(INTEGER_D_BASE10, byteValue, shortValue, intValue, longValue);\n\t}\n\n\t@Test\n\tpublic void e_for_exponential_number() {\n\t\tSystem.out.printf(EXPONENTIAL_E, floatValue);\n\t}\n\n\t@Test\n\tpublic void f_for_decimal() {\n\t\tSystem.out.printf(DECIMAL_F, doubleValue, floatValue);\n\t}\n\n\t@Test\n\tpublic void o_for_integer_base8() {\n\t\tSystem.out.printf(INTEGER_O_BASE8, byteValue, shortValue, intValue, longValue);\n\t}\n\n\t@Test\n\tpublic void padding_space() {\n\t\t\/\/ % 10.3f - Format a decimal with padding empty space: 125.100\n\t\tSystem.out.printf(DECIMAL_PADDING_BLANK, 125.1f);\n\t}\n\n\t@Test\n\tpublic void padding_zero() {\n\t\t\/\/ %010.3f - Format a decimal with padding zero: 000125.100\n\t\tSystem.out.printf(DECIMAL_PADDING_ZERO, 125.1f);\n\t}\n\n\t@Test\n\tpublic void with_all_formatting_flags_width_precision() {\n\t\t\/\/ %-+,10.2f - Format a negative number by left-justified, separating with comma,\n\t\t\/\/ with a sign, 10 width, and 2 precision: -12,345.12\n\t\tSystem.out.printf(DECIMAL_FLAGS_WIDTH_PRECISION, -12345.1234f);\n\t}\n\n\t@Test\n\tpublic void x_for_integer_base16() {\n\t\tSystem.out.printf(INTEGER_X_BASE16, byteValue, shortValue, intValue, longValue);\n\t}\n\n}\n<\/pre>\nExecute mvn test -Dtest=Printf_NumberTest<\/code> and capture the output. <\/p>\nPrintf_NumberTest results<\/em><\/span><\/p>\nC:\\MaryZheng\\Workspaces\\jdk12\\java-printf-demo>mvn test -Dtest=Printf_NumberTest\n[INFO] Scanning for projects...\n[INFO]\n[INFO] -----------------< java-printf-demo:java-printf-demo >------------------\n[INFO] Building java-printf-demo 0.0.1-SNAPSHOT\n[INFO] --------------------------------[ jar ]---------------------------------\n[INFO]\n[INFO] --- maven-resources-plugin:2.6:resources (default-resources) @ java-printf-demo ---\n[WARNING] Using platform encoding (Cp1252 actually) to copy filtered resources, i.e. build is platform dependent!\n[INFO] skip non existing resourceDirectory C:\\MaryZheng\\Workspaces\\jdk12\\java-printf-demo\\src\\main\\resources\n[INFO]\n[INFO] --- maven-compiler-plugin:3.8.0:compile (default-compile) @ java-printf-demo ---\n[INFO] Changes detected - recompiling the module!\n[WARNING] File encoding has not been set, using platform encoding Cp1252, i.e. build is platform dependent!\n[INFO] Compiling 7 source files to C:\\MaryZheng\\Workspaces\\jdk12\\java-printf-demo\\target\\classes\n[INFO]\n[INFO] --- maven-resources-plugin:2.6:testResources (default-testResources) @ java-printf-demo ---\n[WARNING] Using platform encoding (Cp1252 actually) to copy filtered resources, i.e. build is platform dependent!\n[INFO] skip non existing resourceDirectory C:\\MaryZheng\\Workspaces\\jdk12\\java-printf-demo\\src\\test\\resources\n[INFO]\n[INFO] --- maven-compiler-plugin:3.8.0:testCompile (default-testCompile) @ java-printf-demo ---\n[INFO] Nothing to compile - all classes are up to date\n[INFO]\n[INFO] --- maven-surefire-plugin:2.12.4:test (default-test) @ java-printf-demo ---\n[INFO] Surefire report directory: C:\\MaryZheng\\Workspaces\\jdk12\\java-printf-demo\\target\\surefire-reports\n\n-------------------------------------------------------\n T E S T S\n-------------------------------------------------------\nRunning jcg.zheng.demo.Printf_NumberTest\n\nTestMethodName:d_for_integer_base10\n%d - byteValue is: 12, shortValue is: 121, intValue is: 123, longValue is: 1234567.\nTestMethodName:x_for_integer_base16\n%x - Base 16. byteValue is: c, shortValue is: 79, intValue is: 7b, longValue is: 12d687.\nTestMethodName:o_for_integer_base8\n%o - Octal format. byteValue is: 14, shortValue is: 171, intValue is: 173, longValue is: 4553207.\nTestMethodName:e_for_exponential_number\n%e - exponential number. Value is: 1.234500e+02.\nTestMethodName:f_for_decimal\n%f - doubleValue is: 10.123000. floatValue is: 123.449997\nTestMethodName:with_all_formatting_flags_width_precision\n%-+,10.2f - Format a negative number by left-justified, separating with comma, with a sign, 10 width, and 2 precision: -12,345.12\nTestMethodName:padding_zero\n%010.3f - Format a decimal with padding zero: 000125.100\nTestMethodName:padding_space\n% 10.3f - Format a decimal with padding empty space: 125.100\nTestMethodName:explicit_indexing_test_differentOrder\nexplicit two arguments: Ni, Hao!\nTestMethodName:relative_indexing_test\nrelative arguments - Zheng, Zheng, Zheng, Mary, and Mary\nTestMethodName:explicit_indexing_test\nexplicit two arguments: Hello, World!\nTestMethodName:ordinary_indexing_test_exception\nthrow MissingFormatArgumentException: test, Tests run: 12, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 0.193 sec\n\nResults :\n\nTests run: 12, Failures: 0, Errors: 0, Skipped: 0\n\n[INFO] ------------------------------------------------------------------------\n[INFO] BUILD SUCCESS\n[INFO] ------------------------------------------------------------------------\n[INFO] Total time: 8.983 s\n[INFO] Finished at: 2019-07-07T11:52:47-05:00\n[INFO] ------------------------------------------------------------------------\n\nC:\\MaryZheng\\Workspaces\\jdk12\\java-printf-demo><\/pre>\n4.2 NumberFormatTest<\/h3>\n
Java provides a NumberFormat<\/a> class to format a number. In this step, I will create several test methods to format a number. It achieves similar formatting results as the printf<\/code> method with more readable code.<\/p>\nNumberFormatTest.java<\/em><\/span> <\/p>\npackage jcg.zheng.demo;\n\nimport static org.junit.Assert.assertEquals;\n\nimport java.text.NumberFormat;\nimport java.util.Locale;\n\nimport org.junit.Test;\n\npublic class NumberFormatTest {\n\n\tprivate NumberFormat usNumFormat = NumberFormat.getInstance(new Locale(\"en\", \"US\"));;\n\n\t@Test\n\tpublic void formatDecimal() {\t \n\t\tusNumFormat.setMaximumFractionDigits(4);\n\t\tusNumFormat.setMinimumFractionDigits(2);\n\t \n\t\tassertEquals(\"123.4568\", usNumFormat.format(123.45678));\n\t}\n\n\t@Test\n\tpublic void formatInteger() {\n\t\tassertEquals(\"100\", usNumFormat.format(100l));\n\t}\n\n\t@Test\n\tpublic void formatPercentage() {\n\t\tNumberFormat nf = NumberFormat.getPercentInstance();\n\t \n\t\tassertEquals(\"25%\", nf.format(0.25));\n\t}\n\n}\n<\/pre>\nExecute mvn test -Dtest=NumberFormatTest<\/code> and capture the output. <\/p>\nNumberFormatTest Output<\/em><\/span>\n<\/p>\n-------------------------------------------------------\n T E S T S\n-------------------------------------------------------\nRunning jcg.zheng.demo.NumberFormatTest\nTests run: 3, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 0.174 sec\n\nResults :\n\nTests run: 3, Failures: 0, Errors: 0, Skipped: 0<\/pre>\n5. Format a Date<\/h2>\n5.1 Printf_DateTest<\/h3>\n
Java provides additional specifier suffix after the date\/time conversation specifiers: t<\/code> and T<\/code>. <\/p>\nHere are some common date suffix specifiers:<\/p>\n
\nm<\/code> – Month, formatted as two digits with leading zeros as necessary, i.e. 01 – 12<\/li>\nd<\/code> – Day of month, formatted as two digits with leading zeros as necessary, i.e. 01 – 31<\/li>\ny<\/code> – Last two digits of the year, formatted with leading zeros as necessary, i.e. 00 – 99<\/li>\nY<\/code> – Year, formatted to at least four digits with leading zeros as necessary, e.g. 0092 equals 92 CE for the Gregorian calendar <\/li>\n<\/ul>\nHere are some common time suffix specifiers:<\/p>\n
\nH<\/code> – Hour of the day for the 24-hour clock, formatted as two digits with a leading zero as necessary i.e. 00 – 23.<\/li>\nM<\/code> – Minute within the hour formatted as two digits with a leading zero as necessary, i.e. 00 – 59.<\/li>\nS<\/code> – Seconds within the minute, formatted as two digits with a leading zero as necessary, i.e. 00 – 60 (“60” is a special value required to support leap seconds).<\/li>\nr<\/code> – a 12-hour clock time as \"%tI:%tM:%tS %Tp\"<\/code> <\/li>\n<\/ul>\nIn this step, I will create several test methods to format a date with the predefined format specifiers, using again the System.out.printf method. <\/p>\n
\n- Format a data time with
tc<\/code><\/li>\n- format a date with
tD<\/code><\/li>\n- format a ISO8601 date with
tF<\/code><\/li>\n- Format a 12 hour time with
tr<\/code><\/li>\n<\/ul>\nPrintf_DateTest.java<\/em><\/span> <\/p>\npackage jcg.zheng.demo;\n\nimport java.util.Date;\n\nimport org.junit.Test;\n\npublic class Printf_DateTest extends PrintfFormatBaseTest {\n\n\t@Test\n\tpublic void tc_detail_date_time() {\n\t\t\/\/ DateTime: Mon Jul 01 23:09:59 CDT 2019\n\t\tSystem.out.printf(\"DateTime: %1$tc\", new Date());\n\t}\n\t\n\t@Test\n\tpublic void Tc_detail_date_time() {\n\t\t\/\/ DateTime: SUN JUL 07 07:19:32 CDT 2019\n\t\tSystem.out.printf(\"DateTime: %1$Tc\", new Date());\n\t}\n\n\t@Test\n\tpublic void tD_month_day_year() {\n\t\t\/\/ Date: 07\/01\/19\n\t\tSystem.out.printf(\"Date: %1$tD\", new Date());\n\t}\n\n\n\t@Test\n\tpublic void dateTime_format_explicating_indexing() {\n\t\t\/\/ Time: 01-07-2019 22:54:31\n\t\t\/\/ td day of month\n\t\tSystem.out.printf(\"Time: %1$td-%1$tm-%1$tY %1$tH:%1$tM:%1$tS\", new Date());\n\t}\n\n\t@Test\n\tpublic void dateTime_format_explicating_indexing_2() {\n\t\t\/\/ Date: July 01 2019\n\t\t\/\/ tB local-specific full month name\n\t\tSystem.out.printf(\"Date: %1$tB %1$td %1$tY\", new Date());\n\t}\n\n\t@Test\n\tpublic void tF_ISO8601() {\n\t\t\/\/ Date: 2019-07-01\n\t\tSystem.out.printf(\"Date: %1$tF\", new Date());\n\t}\n\n\t@Test\n\tpublic void tR_Hour_Minute() {\n\t\t\/\/ tH:tM\n\t\tSystem.out.printf(\"Date: %1$tR\", new Date());\n\t}\n\n\t@Test\n\tpublic void tr_Hour_Minute_Second_12() {\n\t\t\/\/ Time: 11:07:18 PM\n\t\t\/\/ tH:tM:tS\n\t\tSystem.out.printf(\"Time: %1$tr\", new Date());\n\t}\n\n\t@Test\n\tpublic void tT_Hour_Minute_Second() {\n\t\t\/\/ tH:tM:tS\n\t\tSystem.out.printf(\"Date: %1$tT\", new Date());\n\t}\n}\n<\/pre>\nExecute mvn test -Dtest=Printf_DateTest<\/code> and capture the output. <\/p>\nPrintf_DateTest Output<\/em><\/span>\n<\/p>\nRunning jcg.zheng.demo.Printf_DateTest\n\nTestMethodName:tr_Hour_Minute_Second_12\nTime: 12:00:29 PM\nTestMethodName:tR_Hour_Minute\nDate: 12:00\nTestMethodName:dateTime_format_explicating_indexing_2\nDate: July 07 2019\nTestMethodName:dateTime_format_explicating_indexing\nTime: 07-07-2019 12:00:29\nTestMethodName:tD_month_day_year\nDate: 07\/07\/19\nTestMethodName:tc_detail_date_time\nDateTime: Sun Jul 07 12:00:29 CDT 2019\nTestMethodName:tT_Hour_Minute_Second\nDate: 12:00:29\nTestMethodName:Tc_detail_date_time\nDateTime: SUN JUL 07 12:00:29 CDT 2019\nTestMethodName:tF_ISO8601\nDate: 2019-07-07\nTestMethodName:explicit_indexing_test_differentOrder\nexplicit two arguments: Ni, Hao!\nTestMethodName:relative_indexing_test\nrelative arguments - Zheng, Zheng, Zheng, Mary, and Mary\nTestMethodName:explicit_indexing_test\nexplicit two arguments: Hello, World!\nTestMethodName:ordinary_indexing_test_exception\nthrow MissingFormatArgumentException: test, Tests run: 13, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 0.364 sec\n\nResults :\n\nTests run: 13, Failures: 0, Errors: 0, Skipped: 0\n<\/pre>\n5.2 DateFormatTest<\/h3>\n
Java provides a SimpleDateFormat<\/a> and DateTimeFormatter<\/a> class to format a date. Both classes have similar format specifiers, but the DateTimeFormatter<\/code> class provides static constants for the common formatting patterns. In this step, I will create two test methods to show how to format a date.<\/p>\nDateFormatTest.java<\/em><\/span> <\/p>\npackage jcg.zheng.demo;\n\nimport java.text.DateFormat;\nimport java.text.SimpleDateFormat;\nimport java.time.LocalDateTime;\nimport java.time.format.DateTimeFormatter;\nimport java.util.GregorianCalendar;\n\nimport org.junit.Test;\n\npublic class DateFormatTest {\n\n\t@Test\n\tpublic void dateTimeFormat() {\n\t\tDateFormat df = new SimpleDateFormat(\"dd-MM-yyyy hh:mm:ss\");\n\n\t\tSystem.out.println(df.format((new GregorianCalendar()).getTime()));\n\t}\n\n\t@Test\n\tpublic void DateTimeFormatter_java8() {\n\t\tDateTimeFormatter formatter = DateTimeFormatter.ISO_DATE_TIME;\n\n\t\tLocalDateTime now = LocalDateTime.now();\n\t\tSystem.out.println(\"default format:\" + now);\n\n\t\tString formatDateTime = now.format(formatter);\n\n\t\tSystem.out.println(\"ISO_DATE_TIME format : \" + formatDateTime);\n\t}\n\n}\n<\/pre>\n Execute mvn test -Dtest=DateFormatTest<\/code> and capture the output. <\/p>\nDateFormatTest Output<\/em><\/span>\n<\/p>\n-------------------------------------------------------\n T E S T S\n-------------------------------------------------------\nRunning jcg.zheng.demo.DateFormatTest\ndefault format:2019-07-07T12:03:39.023577700\nISO_DATE_TIME format : 2019-07-07T12:03:39.0235777\n07-07-2019 12:03:39\nTests run: 2, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 0.242 sec\n\nResults :\n\nTests run: 2, Failures: 0, Errors: 0, Skipped: 0<\/pre>\n6. Format a String <\/h2>\n6.1 Printf_StringTest<\/h3>\n
In this step, I will create several Junit test methods to format a string with several conversion specifiers: %c, %b, %h, %s, and %S.<\/p>\n
Printf_StringTest.java<\/em><\/span> <\/p>\npackage jcg.zheng.demo;\n\nimport java.io.UnsupportedEncodingException;\n\nimport org.junit.Test;\n\npublic class Printf_StringTest extends PrintfFormatBaseTest {\n\n\tprivate boolean isFalse = false;\n\tprivate Boolean isTrue = Boolean.TRUE;\n\n\t@Test\n\tpublic void b_for_boolean() throws UnsupportedEncodingException {\n\t\tSystem.out.printf(BOOLEAN_B, isFalse, isTrue);\n\t}\n\t\n\t@Test\n\tpublic void b_for_String_always_True() throws UnsupportedEncodingException {\n\t\tSystem.out.printf(BOOLEAN_B, \"test\", 1);\n\t}\n\n\t@Test\n\tpublic void c_for_character() {\n\t\tSystem.out.printf(CHAR_C, 'm', 'm');\n\t}\n\n\t@Test\n\tpublic void h_for_hashcode() {\n\t\tString s = \"Hello World\";\n\t\tInteger number = Integer.valueOf(100);\n\t\tSystem.out.printf(HASHCODE_H, s, number);\n\n\t}\n\n\t@Test\n\tpublic void n_for_newline() {\n\t\tSystem.out.printf(\"Hello World%n2nd line\");\n\t}\n\n\t@Test\n\tpublic void s_for_string() {\n\t\tString stringVal = \"Hi, Mary!\";\n\t\tSystem.out.printf(\"Left-justified is: %-20s\\n\", stringVal);\n\t\tSystem.out.printf(\"Uppercase, Right-justified is: %20S\\n\", stringVal);\n\t}\n\n\t@Test\n\tpublic void s_for_string_width_too_small() {\n\t\tString stringVal = \"Hi, Mary!\";\n\t\tSystem.out.printf(\"width is smaller: %2S\", stringVal);\n\t}\n\n}\n<\/pre>\n Execute mvn test -Dtest=Printf_StringTest<\/code> and capture the output. <\/p>\nPrintf_StringTest Output<\/em><\/span>\n<\/p>\nRunning jcg.zheng.demo.Printf_StringTest\n\nTestMethodName:b_for_String_always_True\n%b - format boolean value: true, %B - Boolean value: TRUE\nTestMethodName:s_for_string_width_too_small\nwidth is smaller: HI, MARY!\nTestMethodName:n_for_newline\nHello World\n2nd line\nTestMethodName:h_for_hashcode\nThe string object's hashcode: cc969a84, the interger's hashcode: 64\nTestMethodName:b_for_boolean\n%b - format boolean value: false, %B - Boolean value: TRUE\nTestMethodName:s_for_string\nLeft-justified is: Hi, Mary!\nUppercase, Right-justified is: HI, MARY!\n\nTestMethodName:c_for_character\n%c - format char with lower-case value: m, %C - with upper-case value: M.\nTestMethodName:explicit_indexing_test_differentOrder\nexplicit two arguments: Ni, Hao!\nTestMethodName:relative_indexing_test\nrelative arguments - Zheng, Zheng, Zheng, Mary, and Mary\nTestMethodName:explicit_indexing_test\nexplicit two arguments: Hello, World!\nTestMethodName:ordinary_indexing_test_exception\nthrow MissingFormatArgumentException: test, Tests run: 11, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 0.211 sec\n\nResults :\n\nTests run: 11, Failures: 0, Errors: 0, Skipped: 0<\/pre>\n6.2 Printf_FileTest<\/h3>\n
In this step, I will demonstrate how to write the formatted data to a text file with the printf<\/code> method.<\/p>\nPrintf_FileTest.java<\/em><\/span> <\/p>\npackage jcg.zheng.demo;\n\nimport java.io.FileNotFoundException;\nimport java.io.FileOutputStream;\nimport java.io.PrintStream;\nimport java.util.Date;\n\nimport org.junit.Test;\n\npublic class Printf_FileTest extends PrintfFormatBaseTest {\n\n\t@Test\n\tpublic void writetoFile() {\n\t\tPrintStream writeToFile;\n\t\ttry {\n\t\t\twriteToFile = new PrintStream(new FileOutputStream(\"Printf_demo.txt\", true));\n\n\t\t\twriteToFile.printf(BOOLEAN_B, false, Boolean.TRUE);\n\t\t\twriteToFile.printf(NEW_LINE);\n\t\t\twriteToFile.printf(CHAR_C, 'a', 'a');\n\t\t\twriteToFile.printf(NEW_LINE);\n\t\t\t\n\t\t\twriteToFile.printf(\"%%-20s - Format string with Left-justified and 20 width is: %-20s\", \"Mary Zheng\");\n\t\t\twriteToFile.printf(NEW_LINE);\n\t\t\twriteToFile.printf(\"%%20S - Format string with Uppercase, Right-justified : %20S\", \"Hello\");\n\t\t\twriteToFile.printf(NEW_LINE);\n\t\t\twriteToFile.printf(DECIMAL_F, doubleValue, floatValue);\n\t\t\twriteToFile.printf(NEW_LINE);\n\t\t\twriteToFile.printf(EXPONENTIAL_E, floatValue);\n\t\t\twriteToFile.printf(NEW_LINE);\n\t\t\twriteToFile.printf(INTEGER_D_BASE10, byteValue, shortValue, intValue, longValue);\n\t\t\twriteToFile.printf(NEW_LINE);\n\t\t\twriteToFile.printf(INTEGER_O_BASE8, byteValue, shortValue, intValue, longValue);\t\t\n\t\t\twriteToFile.printf(NEW_LINE);\n\t\t\twriteToFile.printf(INTEGER_X_BASE16, byteValue, shortValue, intValue, longValue);\n\t\t\twriteToFile.printf(NEW_LINE);\n\t\t\twriteToFile.printf(DECIMAL_PADDING_BLANK, 125.1f);\n\t\t\twriteToFile.printf(NEW_LINE);\n\t\t\twriteToFile.printf(DECIMAL_PADDING_ZERO, 125.1f);\n\t\t\twriteToFile.printf(NEW_LINE);\n\t\t\twriteToFile.printf(DECIMAL_FLAGS_WIDTH_PRECISION, -12345.1234f);\n\t\t\twriteToFile.printf(NEW_LINE);\n\n\t\t\twriteToFile.printf(\"%%1$tc - Format a DateTime: %1$tc\", new Date());\n\t\t\twriteToFile.printf(NEW_LINE);\n\t\t\twriteToFile.printf(\"%%1$tD - Format a Date: %1$tD\", new Date());\n\t\t\twriteToFile.printf(NEW_LINE);\t\t \n\t\t\twriteToFile.printf(\"%%1$tT - Format a Time: %1$tT\", new Date());\n\t\t\twriteToFile.printf(NEW_LINE);\n\t\t \n\t\t} catch (FileNotFoundException e) {\n\t\t\te.printStackTrace();\n\t\t}\n\n\t}\n\n}\n<\/pre>\nExecute mvn test -Dtest=Printf_FileTest<\/code> and capture the content of Printf_demo.txt<\/code>. <\/p>\nPrintf_demo.txt<\/em><\/span>\n<\/p>\n%b - format boolean value: false, %B - Boolean value: TRUE\n%c - format char with lower-case value: a, %C - with upper-case value: A.\n%-20s - Format string with Left-justified and 20 width is: Mary Zheng \n%20S - Format string with Uppercase, Right-justified : HELLO\n%f - doubleValue is: 10.123000. floatValue is: 123.449997\n%e - exponential number. Value is: 1.234500e+02.\n%d - byteValue is: 12, shortValue is: 121, intValue is: 123, longValue is: 1234567.\n%o - Octal format. byteValue is: 14, shortValue is: 171, intValue is: 173, longValue is: 4553207.\n%x - Base 16. byteValue is: c, shortValue is: 79, intValue is: 7b, longValue is: 12d687.\n% 10.3f - Format a decimal with padding empty space: 125.100\n%010.3f - Format a decimal with padding zero: 000125.100\n%-+,10.2f - Format a negative number by left-justified, separating with comma, with a sign, 10 width, and 2 precision: -12,345.12\n%1$tc - Format a DateTime: Sun Jul 07 12:06:42 CDT 2019\n%1$tD - Format a Date: 07\/07\/19\n%1$tT - Format a Time: 12:06:42\n<\/pre>\n7. Printf Java Example \u2013 Summary<\/h2>\n
In this example, I demonstrated how to use the printf<\/code> method to:<\/p>\n\n- Format a number<\/li>\n
- Format a date<\/li>\n
- Format a string<\/li>\n
- Write to a file<\/li>\n<\/ul>\n
I also compared printf<\/code> to NumberFormat<\/code>, SimpleDateFormat<\/code>, and DateTimeFormatter<\/code>. It is important for the developers to know the printf format specifiers when using the System.out.printf method.<\/p>\n8. More articles<\/h2>\n\n- Java Tutorial for Beginners<\/a><\/li>\n
- ArrayList Java Example \u2013 How to use arraylist<\/a><\/li>\n
- Hashmap Java Example<\/a><\/li>\n
- Java Array \u2013 java.util.Arrays Example (with Video)<\/a><\/li>\n
- Java String Class Example<\/a><\/li>\n
- Java List Example<\/a><\/li>\n
- java.util.Scanner \u2013 Scanner Java Example<\/a><\/li>\n
- Java Map Example<\/a><\/li>\n
- Java Queue Example<\/a><\/li>\n
- Java Stack Example<\/a><\/li>\n<\/ul>\n
9. Download the Source Code<\/h2>\n
This was an example on Java printf() Method . This example consists of a Maven project which defines seven test classes to demonstrate the printf<\/code> method’s usages.<\/p>\n