Java – after reasoning, l must be specified as long, F and D as float and double

Here are a few related questions

According to the title, why should you specify the variable type as long or float, double? Does the compiler not evaluate variable types?

Java believes that all integer literals are ints - is this to reduce the blow of unintentional memory waste? Double all floating-point text to ensure maximum accuracy?

Solution

When you have a constant, it looks the same, but there is no subtle difference between the values In addition, due to the introduction of automatic packing function, you get different results

Consider that if you multiply 0.1 by 0.1 as a floating-point number or double value and convert it to a floating-point number, you can get this value

float a = (float) (0.1 * 0.1);
float b = 0.1f * 0.1f;
System.out.println("a= "+new BigDecimal(a));
System.out.println("b= "+new BigDecimal(b));
System.out.println("a == b is " + (a == b));

print

a= 0.00999999977648258209228515625
b= 0.010000000707805156707763671875
a == b is false

Now compare the results of a calculation you performed using float or int

float a = 33333333f - 11111111f;
float b = 33333333 - 11111111;
System.out.println("a= "+new BigDecimal(a));
System.out.println("b= "+new BigDecimal(b));
System.out.println("a == b is " + (a == b));

print

a= 22222220
b= 22222222
a == b is false

Compare int and long

long a = 33333333 * 11111111; // overflows
long b = 33333333L * 11111111L;
System.out.println("a= "+new BigDecimal(a));
System.out.println("b= "+new BigDecimal(b));
System.out.println("a == b is " + (a == b));

print

a= -1846840301
b= 370370362962963
a == b is false

More double length

double a = 333333333333333333L  / 333333333L;
double b = 333333333333333333D  / 333333333D;
System.out.println("a= "+new BigDecimal(a));
System.out.println("b= "+new BigDecimal(b));
System.out.println("a == b is " + (a == b));

print

a= 1000000001
b= 1000000000.99999988079071044921875
a == b is false

In short, using int, long, double, or float may produce different results than using other types