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Java String format Method - Java 147

Java String format Method – Java 147

Java String format Method

指定的格式字串和參數返回格式化的字串，可以使用此方法連接字串，格式化輸出連接的字串，如果格式為空，會拋出 NullPointerException ，如果指定的格式不合法或參數不足，會拋出 IllegalFormatException ，類似 c 語言的 sprintf 方法和 java 的 printf 方法， Format String Java 本篇增加了範例，並透過單元測試來驗證產出結果。

檔案目錄

./
   +- src
       +- test
       |   +- org
       |       +- ruoxue
       |           +- java_147
       |               +- string
       |                   +- StringFormatTest.java

單元測試

Java Format String 提供格式化字串、整數、浮點數及填充等操作。

string

格式化字串，及長度為 10 向右對齊。

	@Test
	public void string() {
		String value = "Java 147";
		String formatted = String.format("String is: %s", value);
		System.out.println(formatted);
		formatted = String.format("String is: %10s", value);
		System.out.println(formatted);
	}
String is: Java 147
String is:   Java 147

charz

格式化字元，及長度為 10 向右對齊。

	@Test
	public void charz() {
		char value = 'J';
		String formatted = String.format("Char is: %c", value);
		System.out.println(formatted);

		formatted = String.format("Char is: %10c", value);
		System.out.println(formatted);
	}
Char is: J
Char is:          J

bolleanz

Java Format String 格式化布林，及長度為 10 向右對齊。

	@Test
	public void bolleanz() {
		boolean value = true;
		String formatted = String.format("Boolean is: %b", value);
		System.out.println(formatted);

		value = false;
		formatted = String.format("Boolean is: %10b", value);
		System.out.println(formatted);
	}
Boolean is: true
Boolean is:      false

integer

Java Format String 格式化整數支援多種資料類型，將其格式化為字串類型。

	@Test
	public void integer() {
		byte byteValue = Byte.MAX_VALUE;
		String formatted = String.format("Byte is: %d", byteValue);
		System.out.println(formatted);

		short shortValue = Short.MAX_VALUE;
		formatted = String.format("Short is: %d", shortValue);
		System.out.println(formatted);

		int intValue = Integer.MAX_VALUE;
		formatted = String.format("Integer is: %d", intValue);
		System.out.println(formatted);

		long longValue = Long.MAX_VALUE;
		formatted = String.format("Long is: %d", longValue);
		System.out.println(formatted);

		BigInteger bigIntegerValue = BigInteger.ZERO;
		formatted = String.format("BigInteger is: %d", bigIntegerValue);
		System.out.println(formatted);
	}

Byte is: 127
Short is: 32767
Integer is: 2147483647
Long is: 9223372036854775807
BigInteger is: 0

hex

格式化整數為 16 進位字串，及長度為 10 向右對齊。

	@Test
	public void hex() {
		int intValue = Integer.MAX_VALUE;
		String formatted = String.format("Hex is: %x", intValue);
		System.out.println(formatted);
		
		formatted = String.format("Hex is: %10x", intValue);
		System.out.println(formatted);
		
		formatted = String.format("Hex is: %010x", intValue);
		System.out.println(formatted);

	}
Hex is: 7fffffff
Hex is:   7fffffff
Hex is: 007fffffff

floating

格式化浮點數，及長度為 10 向右對齊。

	@Test
	public void floating() {
		float floatValue = Float.MAX_VALUE;
		String formatted = String.format("Float is: %f", floatValue);
		System.out.println(formatted);

		floatValue = 1.47f;
		formatted = String.format("Float is: %10.4f", floatValue);
		System.out.println(formatted);

		double doubleValue = Double.MAX_VALUE;
		formatted = String.format("Double is: %e", doubleValue);
		System.out.println(formatted);
	}
Float is: 340282346638528860000000000000000000000.000000
Float is:     1.4700
Double is: 1.797693e+308

padding

格式化整數，及長度為 10 向右或向左對齊，填充 0 。

	@Test
	public void padding() {
		int intValue = 147;
		String formatted = String.format("%010d", intValue);
		System.out.println(formatted);

		formatted = String.format("% d", intValue);
		System.out.println(formatted);

		formatted = String.format("%10d", intValue);
		System.out.println(formatted);

		formatted = String.format("%-10d", intValue);
		System.out.println(formatted);
	}

0000000147
 147
       147
147

StringFormatTest.java

String Format in Java 新增單元測試，驗證是否符合預期。

package org.ruoxue.java_147.string;

import java.math.BigInteger;

import org.junit.Test;

public class StringFormatTest {

	@Test
	public void string() {
		String value = "Java 147";
		String formatted = String.format("String is: %s", value);
		System.out.println(formatted);
		formatted = String.format("String is: %10s", value);
		System.out.println(formatted);
	}

	@Test
	public void charz() {
		char value = 'J';
		String formatted = String.format("Char is: %c", value);
		System.out.println(formatted);

		formatted = String.format("Char is: %10c", value);
		System.out.println(formatted);
	}

	@Test
	public void bolleanz() {
		boolean value = true;
		String formatted = String.format("Boolean is: %b", value);
		System.out.println(formatted);

		value = false;
		formatted = String.format("Boolean is: %10b", value);
		System.out.println(formatted);
	}

	@Test
	public void integer() {
		byte byteValue = Byte.MAX_VALUE;
		String formatted = String.format("Byte is: %d", byteValue);
		System.out.println(formatted);

		short shortValue = Short.MAX_VALUE;
		formatted = String.format("Short is: %d", shortValue);
		System.out.println(formatted);

		int intValue = Integer.MAX_VALUE;
		formatted = String.format("Integer is: %d", intValue);
		System.out.println(formatted);

		long longValue = Long.MAX_VALUE;
		formatted = String.format("Long is: %d", longValue);
		System.out.println(formatted);

		BigInteger bigIntegerValue = BigInteger.ZERO;
		formatted = String.format("BigInteger is: %d", bigIntegerValue);
		System.out.println(formatted);
	}

	@Test
	public void hex() {
		int intValue = Integer.MAX_VALUE;
		String formatted = String.format("Hex is: %x", intValue);
		System.out.println(formatted);
		
		formatted = String.format("Hex is: %10x", intValue);
		System.out.println(formatted);
		
		formatted = String.format("Hex is: %010x", intValue);
		System.out.println(formatted);

	}

	@Test
	public void floating() {
		float floatValue = Float.MAX_VALUE;
		String formatted = String.format("Float is: %f", floatValue);
		System.out.println(formatted);

		floatValue = 1.47f;
		formatted = String.format("Float is: %10.4f", floatValue);
		System.out.println(formatted);

		double doubleValue = Double.MAX_VALUE;
		formatted = String.format("Double is: %e", doubleValue);
		System.out.println(formatted);
	}

	@Test
	public void padding() {
		int intValue = 147;
		String formatted = String.format("%010d", intValue);
		System.out.println(formatted);

		formatted = String.format("% d", intValue);
		System.out.println(formatted);

		formatted = String.format("%10d", intValue);
		System.out.println(formatted);

		formatted = String.format("%-10d", intValue);
		System.out.println(formatted);
	}
}

心得分享

String Format Java 可以設置任意值的寬度、填充等，提供了幾種 Format 常見方法的操作範例， String Format in Java 支援各種不同類型的格式化，方便簡單的設定，快速產生需要的格式化字串。

原碼下載

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