11

I understand that all of the math functions in java are built in. But I was wondering out of curiosity how Math.min() actually works?

I checked the java documentation and couldn't find anything to help me. I'm quite new to java.

4

5 回答 5

21

int

public static int min(int a, int b) {
    return (a <= b) ? a : b;
}

long

public static long min(long a, long b) {
     return (a <= b) ? a : b;
}

float

public static float min(float a, float b) {
    if (a != a) return a;   // a is NaN
    if ((a == 0.0f) && (b == 0.0f) && (Float.floatToIntBits(b) == negativeZeroFloatBits)) {
         return b;
    }
    return (a <= b) ? a : b;
 }

double

public static double min(double a, double b) {
    if (a != a) return a;   // a is NaN
    if ((a == 0.0d) && (b == 0.0d) && (Double.doubleToLongBits(b) == negativeZeroDoubleBits)) {
        return b;
    }
    return (a <= b) ? a : b;
}

More info: Here

于 2013-09-25T13:32:04.743 回答
10

Java 7 documentation:

Returns the smaller of two int values. That is, the result the argument closer to the value of Integer.MIN_VALUE. If the arguments have the same value, the result is that same value.

Behaviour:

Math.min(1, 2) => 1
Math.min(1F, 2) => 1F
Math.min(3D, 2F) => 2D
Math.min(-0F, 0F) => -0F
Math.min(0D, -0D) => -0D
Math.min(Float.NaN, -2) => Float.NaN
Math.min(-2F, Double.NaN) => Double.NaN

java.lang.Math and java.lang.StrictMath Source:

public static int min(int a, int b) {
    return (a <= b) ? a : b;
}

java.lang.Math Bytecode (javap -c Math.class of Oracle's JDK's JRE's rt.jar):

public static int min(int, int);
Code:
   0: iload_0           // loads a onto the stack
   1: iload_1           // loads b onto the stack
   2: if_icmpgt     9   // pops two ints (a, b) from the stack
                        // and compares them
                        // if b>a, the jvm continues at label 9
                        // else, at the next instruction, 5
                        // icmpgt is for integer-compare-greater-than
   5: iload_0           // loads a onto the stack
   6: goto          10  // jumps to label 10
   9: iload_1           // loads 
  10: ireturn           // returns the currently loaded integer

If the comparison at 5 is true, a will be loaded, the jvm will jump to 10 and return a, if the comparison yields false, it will jump to 9, which will load and return b.

Intrinsics:

This .hpp file of the Java 8 Hotspot JVM hints that it optimizes Math.min even further with optimized machine code:

do_intrinsic(_min, java_lang_Math, min_name, int2_int_signature, F_S)

This means the above bytecode won't be executed by the Java 8 Hotspot JVM. However, this differs from JVM to JVM, which is why I also explained the bytecode!

Hopefully, now you know all there is to know about Math.min! :)

于 2013-09-25T13:40:33.233 回答
3

Just check the Math.java source file :

public static int min(int a, int b) {
    return (a <= b) ? a : b;
}
于 2013-09-25T13:30:00.340 回答
3

Reference

The java.lang.Math.min(int a, int b) returns the smaller of two int values. That is, the result is the value closer to negative infinity. If the arguments have the same value, the result is that same value. If either value is NaN, then the result is NaN. Unlike the numerical comparison operators, this method considers negative zero to be strictly smaller than positive zero. If one argument is positive zero and the other is negative zero, the result is negative zero.

For example

System.out.println(Math.min(1111, 1000));

Output as

1000

It displays minimum value from the Math.min()

于 2013-09-25T13:30:58.093 回答
2

Some efficient form of

math.min(a,b) = public static int min (a, b) {
  if(a<=b) return a;
  else return b;
}
于 2013-09-25T13:30:41.193 回答