Generating a random number, static import process variable parameters of method overloading, comparing floating

A random number generation method

① minimum + Math.random () * (Max - Min 1) : number generated in the range [min, max] 

package com.java1;
import javax.swing.JOptionPane;

public class RandomInt {
   public static void main( String args[] )
   {
      int value;
      String output = "";

      for ( int i = 1; i <= 20; i++ ) {
         value =  (int) ( 1+Math.random() * 6 );
         output += value + "  ";
         
         if ( i % 5 == 0 )
            output += "\n";
      }

      JOptionPane.showMessageDialog( null, output,
         "20 Random Numbers from 1 to 6",
         JOptionPane.INFORMATION_MESSAGE );

      System.exit( 0 );
   }
}

Between the range of the random number generation 1-6

 

 

 ② The new Random (). NextInt (26 ) approach is used to achieve a greater than or equal to 0, a random number less than 26

package com.java1;
import java.util.*;

public class TestRandom
{
    public static void main(String[] args) 
    {
        Random rand = new Random();
        System.out.println("rand.nextBoolean()：" + rand.nextBoolean());
        byte[] buffer = new byte[16];
        rand.nextBytes(buffer);
        System.out.println(Arrays.toString(buffer));
        //生成0.0~1.0之间的伪随机double数
        System.out.println("rand.nextDouble()：" +rand.nextDouble ());
         // generate a pseudorandom number float between 1.0 ~ 0.0 
        System.out.println ( "rand.nextFloat ():" + rand.nextFloat ());
         // generating mean 0.0 the standard deviation is 1.0 gauss pseudo 
        System.out.println ( "rand.nextGaussian ():" + rand.nextGaussian ());
         // generates a pseudo-random integer in the range of long integers 
        System.out.println ( "rand.nextInt ():" + new new . the random () the nextInt ());
         // generate a pseudo-random integer between ~ 26 is 0 
        System.out.println ( "rand.nextInt (26 is):" + rand.nextInt (26 ));
         // generates a long integer in the range of pseudo-random integer 
        System.out.println ( "rand.nextLong ():" +   rand.nextLong ());
    }
}

Answer:

rand.nextBoolean()：true
[103, -90, -76, 58, -91, -52, -23, 45, 50, 73, -43, 70, 77, -64, -48, -122]
rand.nextDouble()：0.1631898380376655
rand.nextFloat()：0.1340416
rand.nextGaussian()：-1.8408133377651577
rand.nextInt()：-382427923
rand.nextInt(26)：3
rand.nextLong()：-1029091829791802274

③ by generating a different seed Random object , and the current time as the seed to generate Random object

package com.java1;
import java.util.Random;

public class TestSeed
{
    public static void main(String[] args)
    {
        Random r1 = new Random(50);
        System.out.println("第一个种子为50的Random对象");
        System.out.println("r1.nextBoolean():\t" + r1.nextBoolean());
        System.out.println("r1.nextInt():\t\t" + r1.nextInt());
        System.out.println("r1.nextDouble():\t" + r1.nextDouble());
        System.out.println("r1.nextGaussian():\t" + r1.nextGaussian());
        System.out.println("---------------------------");
        
        Random r2 = new Random(50);
        System.out.println("第二个种子为50的Random对象");
        System.out.println("r2.nextBoolean():\t" + r2.nextBoolean());
        System.out.println("r2.nextInt():\t\t" + r2.nextInt());
        System.out.println("r2.nextDouble():\t" + r2.nextDouble());
        System.out.println("r2.nextGaussian():\t" + r2.nextGaussian());
        System.out.println("---------------------------");
        
        Random r3 = new Random(100);
        System.out.println("种子为100的Random对象");
        System.out.println("r3.nextBoolean():\t" + r3.nextBoolean());
        System.out.println("r3.nextInt():\t\t" + r3.nextInt());
        System.out.println("r3.nextDouble():\t" + r3.nextDouble());
        System.out.println("r3.nextGaussian():\t" + r3.nextGaussian());
        
       
        Random r4 = new Random(System.currentTimeMillis());
        System.out.println ( "current time as the seed Random object");
        System.out.println("r3.nextBoolean():\t" + r4.nextBoolean());
        System.out.println("r3.nextInt():\t\t" + r4.nextInt());
        System.out.println("r3.nextDouble():\t" + r4.nextDouble());
        System.out.println("r3.nextGaussian():\t" + r4.nextGaussian()); 
    }
}

Output:

The first seed for the Random object 50
r1.nextBoolean (): to true
r1.nextInt (): -1727040520
r1.nextDouble (): .6141579720626675
r1.nextGaussian (): 2.377650302287946
------------ ---------------
the second seed Random object 50
r2.nextBoolean (): to true
r2.nextInt (): -1,727,040,520
r2.nextDouble (): 0.6141579720626675
r2.nextGaussian ( ): 2.377650302287946
---------------------------
seed Random object 100
r3.nextBoolean (): to true
r3.nextInt (): - 1,139,614,796
r3.nextDouble (): .19497605734770518
r3.nextGaussian (): .6762208162903859
the current time as the seed Random object
r3.nextBoolean (): to true
r3.nextInt (): 1678327555
r3.nextDouble (): .16760365386964127
r3.nextGaussian(): -0.7219839638959297

From the results we can know: the same random number seed is produced by the same random number generated at the current time as the seed must be unique.

④ handwritten code to implement random number 1000

According to the formula:

 

 

 Wherein X- _n- seed input = number

 

 

c=0;　　a=7⁵=16807;　　m=Integer.MAX_VALUE;

package com.randseed;
import java.lang.*;
import java.util.Scanner;
public class randseed {
    public static void rand(long x)
    {
        long a;
        for(int i=1;i<=1000;i++)
        {
            a=(x*16807)%Integer.MAX_VALUE;//由公式得
            System.out.println(a);
            x=a;
        }
    }
    
    public static void main(String[] args) {
        In Scanner=new new Scanner (the System.in); 
        System.out.println ( "Please enter the seed number:" );
         Long SEED; 
        SEED = in.nextLong (); 
        RAND (SEED); 
    } 
}

1000 outputs the random number.

Second, static imports

By static import will not have to call: class name method name, but converted to direct the use of the method name invoked.

Here are three ways to solve the problem of absolute value abs

Package com.randseed;
 Import  static java.lang.Math *. ;
 public  class importstatic { 
    
public  static  void Abs ( int A) 
{ 
    IF (A <0 ) 
        A = - A; 
    System.out.println (A); 
} 

    public  static  void main (String [] args) {
         // the TODO Auto-Generated Stub method 
        System.out.println (ABS (-100)); // statically introduced, it is possible to use the direct method 
        System.out.println (Math. ABS (-100)); // mathematical functions Bunsen is a static method 
        Abs (-100);// custom a static approach 
    }
 // three results are the same 
}

Three outputs are: 100

Third, the method of the variable parameter

A method using a variable parameter calculating maximum incoming parameters.

package com.java1;
import java.awt.*;
import java.awt.event.*;
import java.util.*;


public class VariableArgumentsTest{
    
    public static double max(double...values)
    {
        double largest=Double.MIN_VALUE;
        for (double v:values)
            if(v>largest) largest=v;
        return largest;
    }

    public static void main(String args[]) {
    
         System.out.println("Max:"+max(1,11,300,2,3,50,1500,2010,2019));
            
    }
}

The output is: 2019

 Four point method overloading

Heavy Load relationship:

① the same method name

② different types of parameters, number of different parameters, a different order of parameters

Note: The method of the return value is not based on a judgment as

package com.java1;
public class MethodOverload {

    public static void main(String[] args) {
        System.out.println("The square of integer 7 is " + square(7));
        System.out.println("\nThe square of double 7.5 is " + square(7.5));
    }

    public static int square(int x) {
        return x * x;
    }

    public static double square(double y) {
        return y * y;
    }
}

The above code: There are two square method, but different parameter types, and therefore will choose different methods calculations are carried out at the time of call,

Output:

The square of integer 7 is 49

The square of double 7.5 is 56.25

Fifth, compare floating point numbers

In everyday computing will inevitably be used in the comparison of floating-point numbers, but in the comparison between the floating-point numbers can be directly used == it?

Answer: No

== can not be directly used to determine the value of two floating point numbers, but rather to use two numbers Absolute value of less than a very small number , the two numbers are equal.

package com.java1;


public class CompareFloatNumber {

    /**
     * @param args
     */
    public static void main(String[] args) {
        compare();
        compare2();

    }

    private static void compare() {
        double i = 0.0001;
        double j = 0.00010000000000000001;
        System.out.println(i==j);  //输出：true
    }
    private static void compare2() {
        double i = 0.0001;
        double j = 0.000100000000600000001;
        if(Math.abs(i-j)<1e-20){
            System.out.println("true");  
        }
        else
        {
            System.out.println("false");
        }
        
    }

}

Output:

true

false

Therefore, we can not compare to the same integer to floating-point comparison.