Convert double to float in Java

问题:

I am facing an issue related to converting double to float. Actually, I store a float type, 23423424666767, in a database, but when we get data from the database in the below code, getInfoValueNumeric(), it's of double type. The value we get is in the 2.3423424666767E13 form.

So how do we get a float format data like 23423424666767?

2.3423424666767E13 to 23423424666767

public void setInfoValueNumeric(java.lang.Double value) {
    setValue(4, value);
}


@javax.persistence.Column(name = "InfoValueNumeric", precision = 53)
public java.lang.Double getInfoValueNumeric() {
    return (java.lang.Double) getValue(4);
}

回答1:

Just cast your double to a float.

double d = getInfoValueNumeric();
float f = (float)d;

Also notice that the primitive types can NOT store an infinite set of numbers:

float range: from 1.40129846432481707e-45 to 3.40282346638528860e+38
double range: from 1.7e–308 to 1.7e+308

回答2:

I suggest you to retrieve the value stored into the Database as BigDecimal type:

BigDecimal number = new BigDecimal("2.3423424666767E13");

int myInt = number.intValue();
double myDouble = number.doubleValue();

// your purpose
float myFloat = number.floatValue();

BigDecimal provide you a lot of functionalities.

回答3:

Convert Double to Float

public static Float convertToFloat(Double doubleValue) {
    return doubleValue == null ? null : doubleValue.floatValue();
}

Convert double to Float

public static Float convertToFloat(double doubleValue) {
    return (float) doubleValue;
}

回答4:

To answer your query on "How to convert 2.3423424666767E13 to 23423424666767"

You can use a decimal formatter for formatting decimal numbers.

     double d = 2.3423424666767E13;
     DecimalFormat decimalFormat = new DecimalFormat("#");
     System.out.println(decimalFormat.format(d));

Output : 23423424666767

回答5:

Converting from double to float will be a narrowing conversion. From the doc:

A narrowing primitive conversion may lose information about the overall magnitude of a numeric value and may also lose precision and range.

A narrowing primitive conversion from double to float is governed by the IEEE 754 rounding rules (§4.2.4). This conversion can lose precision, but also lose range, resulting in a float zero from a nonzero double and a float infinity from a finite double. A double NaN is converted to a float NaN and a double infinity is converted to the same-signed float infinity.

So it is not a good idea. If you still want it you can do it like:

double d = 3.0;
float f = (float) d;

回答6:

The problem is, your value cannot be stored accurately in single precision floating point type. Proof:

public class test{
    public static void main(String[] args){
        Float a = Float.valueOf("23423424666767");
        System.out.printf("%f\n", a); //23423424135168,000000
        System.out.println(a);        //2.34234241E13
    }
}

Another thing is: you don't get "2.3423424666767E13", it's just the visual representation of the number stored in memory. "How you print out" and "what is in memory" are two distinct things. Example above shows you how to print the number as float, which avoids scientific notation you were getting.

回答7:

First of all, the fact that the value in the database is a float does not mean that it also fits in a Java float. Float is short for floating point, and floating point types of various precisions exist. Java types float and double are both floating point types of different precision. In a database both are called FLOAT. Since double has a higher precision than float, it probably is a better idea not to cast your value to a float, because you might lose precision.

You might also use BigDecimal, which represent an arbitrary-precision number.

回答8:

Use dataType casting. For example:

// converting from double to float:
double someValue;
// cast someValue to float!
float newValue = (float)someValue;

Cheers!

Note:

Integers are whole numbers, e.g. 10, 400, or -5.

Floating point numbers (floats) have decimal points and decimal places, for example 12.5, and 56.7786543.

Doubles are a specific type of floating point number that have greater precision than standard floating point numbers (meaning that they are accurate to a greater number of decimal places).

回答9:

Float.parseFloat(String.valueOf(your_number)