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Convert String to Float in Java with Examples - Java 147

Convert String to Float in Java with Examples – Java 147

Convert String to Float in Java with Examples

將 String 轉換為 float 或 Float 是 Java 中常見的操作，可以使用 DecimalFormat 、 Apache Commons Lang 等方法進行操作， Convert a String to an Float in Java 任務是將該字串轉換為單精度浮點數，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
       |               +- conversion
       |                   +- string
       |                       +- StringToFloatWithExamplesTest.java

單元測試

Convert a String to Float in Java 提供字串轉換成單精度浮點數等操作。

decimalFormat

Convert a String to Float in Java 使用 DecimalFormat 轉換成單精度浮點數。

	@Test
	public void decimalFormat() {
		try {
			String value = "151.88";
			Number number = DecimalFormat.getNumberInstance().parse(value);
			float result = number.floatValue();
			System.out.println(result);
			assertEquals(151.88f, result, 0);

			value = "-40.88";
			number = DecimalFormat.getNumberInstance().parse(value);
			result = number.floatValue();
			System.out.println(result);
			assertEquals(-40.88f, result, 0);

			value = "-$1,240.88";
			DecimalFormat format = new DecimalFormat("$#,##0.00");
			format.setParseBigDecimal(true);

			result = format.parse(value).floatValue();
			System.out.println(result);
			assertEquals(-1240.88f, result, 0);
		} catch (ParseException ex) {
			ex.printStackTrace();
		}
	}
151.88
-40.88
-1240.88

decimalFormatThrowException

Convert a String to Float in Java 使用 DecimalFormat 轉換成單精度浮點數，輸入不合格式的字串，會拋出例外。

	@Test
	public void decimalFormatThrowException() {
		try {
			String value = "151.88";
			Number number = DecimalFormat.getNumberInstance().parse(value);
			float result = number.floatValue();
			System.out.println(result);
			assertEquals(151.88f, result, 0);

			value = "bash-151.88";
			number = DecimalFormat.getNumberInstance().parse(value);
			result = number.floatValue();
			System.out.println(result);
		} catch (ParseException ex) {
			ex.printStackTrace();
		}
	}
151.88
java.text.ParseException: Unparseable number: "bash-151.88"
	at java.text.NumberFormat.parse(NumberFormat.java:385)
	at org.ruoxue.java_147.string.StringToFloatWithExamplesTest.decimalFormatThrowException(StringToFloatWithExamplesTest.java:50)

constructor

Convert a String to Float in Java 使用 Float 建構子，傳入參數字串，建立一個新的 Float 物件。

	@Test
	public void constructor() {
		String value = "151.88";
		float result = new Float(value);
		System.out.println(result);
		assertEquals(151.88f, result, 0);

		value = "-40.88";
		result = new Float(value);
		System.out.println(result);
		assertEquals(-40.88f, result, 0);
	}
151.88
-40.88

constructorThrowException

使用 Float 建構子，傳入參數字串，建立一個新的 Float 物件，輸入不合格式的字串，會拋出例外。

	@Test(expected = NumberFormatException.class)
	public void constructorThrowException() {
		String value = "151.88";
		float result = new Float(value);
		System.out.println(result);
		assertEquals(151.88f, result, 0);

		value = "junit-151.88";
		result = new Float(value);
		System.out.println(result);
	}
151.88
java.lang.NumberFormatException: For input string: "junit-151.88"
	at sun.misc.FloatingDecimal.readJavaFormatString(FloatingDecimal.java:2043)
	at sun.misc.FloatingDecimal.parseFloat(FloatingDecimal.java:122)
	at java.lang.Float.parseFloat(Float.java:451)
	at java.lang.Float.<init>(Float.java:532)
	at org.ruoxue.java_147.string.StringToFloatWithExamplesTest.constructorThrowException(StringToFloatWithExamplesTest.java:79)

NumberUtils_toFloat

使用 Apache Commons Lang – NumberUtils 轉換成單精度浮點數。

	@Test
	public void NumberUtils_toFloat() {
		String value = "151.88";
		float result = NumberUtils.toFloat(value);
		System.out.println(result);
		assertEquals(151.88f, result, 0);

		value = "-40.88";
		result = NumberUtils.toFloat(value);
		System.out.println(result);
		assertEquals(-40.88f, result, 0);

		value = "40.88";
		result = NumberUtils.toFloat(value, 0);
		System.out.println(result);
		assertEquals(40.88f, result, 0);

		value = "junit-151.88";
		result = NumberUtils.toFloat(value, 0);
		System.out.println(result);
		assertEquals(0f, result, 0);
	}
151.88
-40.88
40.88
0.0

StringToFloatWithExamplesTest.java

Java String to Float Examples 新增單元測試，驗證是否符合預期。

package org.ruoxue.java_147.conversion.string;

import static org.junit.Assert.*;

import java.text.DecimalFormat;
import java.text.ParseException;

import org.apache.commons.lang3.math.NumberUtils;
import org.junit.Test;

public class StringToFloatWithExamplesTest {

	@Test
	public void decimalFormat() {
		try {
			String value = "151.88";
			Number number = DecimalFormat.getNumberInstance().parse(value);
			float result = number.floatValue();
			System.out.println(result);
			assertEquals(151.88f, result, 0);

			value = "-40.88";
			number = DecimalFormat.getNumberInstance().parse(value);
			result = number.floatValue();
			System.out.println(result);
			assertEquals(-40.88f, result, 0);

			value = "-$1,240.88";
			DecimalFormat format = new DecimalFormat("$#,##0.00");
			format.setParseBigDecimal(true);

			result = format.parse(value).floatValue();
			System.out.println(result);
			assertEquals(-1240.88f, result, 0);
		} catch (ParseException ex) {
			ex.printStackTrace();
		}
	}

	@Test
	public void decimalFormatThrowException() {
		try {
			String value = "151.88";
			Number number = DecimalFormat.getNumberInstance().parse(value);
			float result = number.floatValue();
			System.out.println(result);
			assertEquals(151.88f, result, 0);

			value = "bash-151.88";
			number = DecimalFormat.getNumberInstance().parse(value);
			result = number.floatValue();
			System.out.println(result);
		} catch (ParseException ex) {
			ex.printStackTrace();
		}
	}

	@Test
	public void constructor() {
		String value = "151.88";
		float result = new Float(value);
		System.out.println(result);
		assertEquals(151.88f, result, 0);

		value = "-40.88";
		result = new Float(value);
		System.out.println(result);
		assertEquals(-40.88f, result, 0);
	}

	@Test(expected = NumberFormatException.class)
	public void constructorThrowException() {
		String value = "151.88";
		float result = new Float(value);
		System.out.println(result);
		assertEquals(151.88f, result, 0);

		value = "junit-151.88";
		result = new Float(value);
		System.out.println(result);
	}

	@Test
	public void NumberUtils_toFloat() {
		String value = "151.88";
		float result = NumberUtils.toFloat(value);
		System.out.println(result);
		assertEquals(151.88f, result, 0);

		value = "-40.88";
		result = NumberUtils.toFloat(value);
		System.out.println(result);
		assertEquals(-40.88f, result, 0);

		value = "40.88";
		result = NumberUtils.toFloat(value, 0);
		System.out.println(result);
		assertEquals(40.88f, result, 0);

		value = "junit-151.88";
		result = NumberUtils.toFloat(value, 0);
		System.out.println(result);
		assertEquals(0f, result, 0);
	}
}

心得分享

Convert a String to an Float in Java with Examples 將 String 實例轉換為 float 或 Float 實例的多種方法， 除了使用 Java 所提供的 DecimalFormat 、 constructor 之外，也有其他選擇使用外部程式庫來轉換成 float ，像是 Apache Commons Lang 等， Java String to Float Examples 提供了幾種常見方法的操作範例。

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