在 Java 中将 double 转换为 float

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最佳答案

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

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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.

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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

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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.

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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;

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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.

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Float.parseFloat(String.valueOf(your_number)

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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;
}

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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).

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This is a nice way to do it:

Double d = 0.5;
float f = d.floatValue();

if you have d as a primitive type just add one line:

double d = 0.5;
Double D = Double.valueOf(d);
float f = D.floatValue();