Saturday, August 10, 2013

How to parse String to Float in Java | Convert Float to String in Java - 3 Examples

float and double are two data type which is used to store floating point values in Java and we often need to convert String to float in Java and sometime even a Float object or float primitive to String. One thing, which is worth remembering about floating point numbers in Java is that they are approximate values, a float value 100.1f may hold actual value as 100.099998, which will be clear, when we seen examples of converting float to String and vice-versa. By the way, It's easy to parse String to float and vice-versa, as rich Java API provides several ways of doing it. If you already familiar with converting String to int or may be String to double in Java, then you can extend same techniques and method to parse float String values. key methods like valueOf() and parseInt(), which is used to parse String to float are overloaded for most primitive data types. If you are particularly interested on rounding of float values, you can use RoundingMode and BigDecimal class, as float and double are always approximate values and comparing two float variable of same values may not always return true, that's why it's advised, not to use float for monetary calculation. In this Java tutorial, we will first see examples of parsing String to float in Java and later converting float to String objects. Remember, we will use float and Float, a wrapper class corresponding to float primitive, interchangeably because by using Java 1.5 autoboxing feature, they are automatically converted to each other, without any Java code. For those, who are still in Java 1.4 or lower version, then can use Float.floatValue() to convert Float wrapper object to float primitive.

3 ways to parse String to float in Java

3 example to convert String to float in JavaThere are mainly three ways to convert String to float value in Java, by using Float.valueOf(), Float.parseFloat() method and by using constructor of Float class, which accepts a String. All these methods throws NumberFormatException if float value is illegal or not parsable. For example trying to convert a String "#200.2" will throw Exception in thread "main" java.lang.NumberFormatException: For input string: "#200.2". By the way it's legal to pass suffix "f" or "F" along with floating point number e.g. "200.2F" will not throw this error.  Similarly, you can also use same technique to parse any negative floating point number String to float in Java, minus sign (-) is permitted in float String. You can use code snippets given in example section  to parse String to float in Java. One thing, which is worth remembering, while dealing with String and float is that, comparing them in String format and as float values may return different result. As shown in following example

float f1 = 414.23f;
float f2 = Float.valueOf("414.23f");
     
String s1 = "414.23f";
String s2 = String.valueOf(f1);
     
boolean result1 = (f1 == f2);
boolean result2 = s1.equals(s2);
System.out.printf("Comparing floating point numbers %f and %f as float"
                             + " returns %b %n", f1, f2, result1);
System.out.printf("Comparing floating point numbers %s and %s as String"
                             + " returns %b %n", s1, s2, result2);

Output:
Comparing floating point numbers 414.230011 and 414.230011 as float returns true
Comparing floating point numbers 414.23f and 414.23 as String returns false


The reason, we get false is because of "f" suffix present in String, which is not very uncommon. Also, it's good idea to remove whitespaces from String before converting them to float in Java.

3 example to convert float to String in Java

Now we know how to parse String to float in Java, it's time to explore second part, converting a float to String. This is even easier than first part. One of the quickest way to get an String object from float value is to concatenate it with an empty String e.g. "" + float, this will give you String object for all your practical purpose. Apart from this nice trick, you also have couple of more tricks on your sleeve, you can either use valueOf() method from java.lang.String class or toString() method from java.lang.Float class, both returns String object. Here is Java program to parse String to floating point number in Java and then convert back float to java.lang.String object. String to Float Conversion Example in Java.

/**
 *
 * Java program to parse String to float in Java and than convert float to
 * String in Java. Remember, while converting same value in float form and in
 * String form will return different result. For example "1".equals("1.0") will
 * return false but 1 == 1.0 may return true.
 *
 * @author Javin Paul
 */
public class StringToFloat {

    public static void main(String args[]) {
     
       // Parsing String to float in Java
       // By using autoboxing Float object can be converted to float primitive
     
       // Converting String to Float using Float.valueOf() method
       String strFloat = "100.1";
       float fValue = Float.valueOf(strFloat);
       System.out.printf("String %s is parse to float %f in Java using valueOf %n"
                            , strFloat, fValue);
     
       // Converting String to Float using Float.parsetFloat() method
       String strFloat2 = "150.15";
       float fValue2 = Float.parseFloat(strFloat2);
       System.out.printf("String %s is converted to float %f in Java using parseFloat %n"
                            , strFloat2, fValue2);
     
       // Parse String to Float Object in Java
       String strFloat3 = "-200.2F";
       Float fValue3 = new Float(strFloat3);
       System.out.printf("String %s is converted to float object %f in Java using"
                            + " Float constructor %n" , strFloat3, fValue3);
     
     
       // Second part - Converting float values to String in Java
       // Converting float data type to String in Java using + operator concatenation
       float fValue4 = 657.2f; // remember f suffix, floating points defaults to double in Java
       String strFloat4 = "" + fValue4;
       System.out.printf("float %f is converted to String %s in Java using"
                            + " concatenation %n" , fValue4, strFloat4);
     
       // Parsing float to String in Java using Float toString method
       Float fValue5 = new Float(786.86f);
       String strFloat5 = fValue5.toString();
       System.out.printf("Float %f is changed to String object %s in Java using"
                            + " toString %n" , fValue5, strFloat5);
     
       // Converting String object to float primitive in Java - valueOf example
       float fValue6 = 919.23f;
       String strFloat6 = String.valueOf(fValue6);
       System.out.printf("float %f is converted to String %s by using valueOf"
                            + " in Java %n" , fValue6, strFloat6);     
    
    }   
 
}

Output:
String 100.1 is parse to float 100.099998 in Java using valueOf
String 150.15 is converted to float 150.149994 in Java using parseFloat
String -200.2F is converted to float object -200.199997 in Java using Float constructor
float 657.200012 is converted to String 657.2 in Java using concatenation
Float 786.859985 is changed to String object 786.86 in Java using toString
float 919.229980 is converted to String 919.23 by using valueOf in Java


That's all on this Java beginners tutorial about parsing String to float in Java and then converting back float values to String objects. We have learned couple of useful tricks for data type conversion, which can be very handy while working on float and String data types together. Just remember, both Float and String are immutable objects  in Java and any modification on this object will result in new object.

1 comment :

Keera said...

Hi Javin, What is the best way to parse String to float in Java? I know all of them can do the job, but which one is the faster, if performance is a concern?

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