Java Learning Notes (math class, Arrays class, BigInteger class, BigDecimal Class)

Math class: Mathematical tools, mathematical calculations, root, logarithm, trigonometric functions, etc.

All methods are static methods, do not need to establish objects, directly called by the class name can be

Example:

Here to write a few in the daily development will be used, such as trigonometric functions usually do not use, understand can

 Packagedemo; Public classMathdemo { Public Static voidMain (string[] args) {function1 ();        Function2 ();        Function3 ();        Function4 ();    Function5 (); }     Public Static voidfunction1 () {inti = Math.Abs (-9);        System.out.println (i); //output: 9, Absolute    }     Public Static voidfunction2 () {DoubleD1 = Math.floor (6.5); DoubleD2 = Math.ceil (6.5); System.out.println (d1);//6.0System.out.println (D2);//7.0    }     Public Static voidFunction3 () {DoubleD1 = Math.pow (2.0, 3.0);        System.out.println (D1); //2 of the 3-time side, output: 8.0        DoubleD2 = MATH.SQRT (4.0);        System.out.println (D2); //4 Development, Output 2.0    }     Public Static voidFunction4 () { for(inti = 0; I < 10; i++) {            DoubleD =Math.random ();            System.out.println (d); //print random number between 0 and 1        }    }     Public Static voidfunction5 () {DoubleD = Math.Round (1.4234);        System.out.println (d); //output 1.0, get rounded value    }}

Arrays class: Array tool classes that help us do some things with arrays:

Some methods can save us a lot of code in daily development

Example:

 Packagedemo;Importjava.util.Arrays; Public classArraysdemo { Public Static voidMain (string[] args) {function1 ();        Function2 ();    Function3 (); }         Public Static voidfunction1 () {//Array in ascending order, here is a lot higher than the bubble sort performance of the fast row        int[] arr = {5,4,8,7,3,1,6};        Arrays.sort (arr);  for(inti = 0; i < arr.length; i++) {System.out.println (arr[i]); }        //Print in ascending order    }         Public Static voidfunction2 () {//array of binary search method, my 6th article has the principle of introduction, and the principle here is roughly the same        int[] arr = {11,4,5,7,9,13,1}; //the premise of dichotomy is an ordered arrayArrays.sort (arr); intindex = Arrays.binarysearch (arr, 7); SYSTEM.OUT.PRINTLN (index);//sorted after 7 of all is 3//Note here: If this element does not exist in the array//then return a negative number: (-insertion point-1)    }         Public Static voidFunction3 () {int[] arr = {1,2,3,4,5}; String String=arrays.tostring (arr);        System.out.println (string); //output: [1, 2, 3, 4, 5] string//The principle was written in my previous articles .    }}

Sometimes an array exceeds the size of a long type and needs to be computed.

BigInteger class: Large number operation

Example:

 Packagedemo;ImportJava.math.BigInteger; Public classBigintegerdemo { Public Static voidMain (string[] args) {function (); }     Public Static voidfunction () {BigInteger B1=NewBigInteger ("6666666666666666666666666666666"); BigInteger B2=NewBigInteger ("1234567891234567891234567891231123123"); BigInteger B3= B1.add (B2);//b1+b2SYSTEM.OUT.PRINTLN (B3);//1234574557901234557901234557897789789BigInteger b4 = b1.subtract (B2);//b1-b2SYSTEM.OUT.PRINTLN (B4);//-1234561224567901224567901224564456457BigInteger B5 = b1.multiply (B2);//b1*b2System.out.println (B5);//A very long number, which is no longer duplicated hereBigInteger B6 = b2.divide (B1);//B2/B1System.out.println (B6);//185185    }}

BigDecimal class: Floating-point large number operation, improve floating-point arithmetic precision

Example:

 Packagedemo;ImportJava.math.BigDecimal; Public classBigdecimaldemo { Public Static voidMain (string[] args) {System.out.println (0.09+0.01);//Output 0.99999System.out.println (1.0-0.32);//Output 0.67999//found that there would be inappropriate results here.//cause: In the computer binary, it means that the floating-point number is inaccurate.//Workaround: BigDecimal classfunction1 ();    Function2 (); }     Public Static voidfunction1 () {BigDecimal B1=NewBigDecimal ("0.09"); BigDecimal B2=NewBigDecimal ("0.01"); BigDecimal B3= B1.add (B2);//b1+b2SYSTEM.OUT.PRINTLN (B3);//get 0.10, rightBigDecimal B4=NewBigDecimal ("1.0"); BigDecimal b5=NewBigDecimal ("0.32"); BigDecimal b6= B4.subtract (B5);//b4-b5System.out.println (B6);//0.68, correctBigDecimal B7= B1.multiply (B2);//b1*b2SYSTEM.OUT.PRINTLN (B7);//0.0009, correct    }     Public Static voidfunction2 () {//There are some differences in division, and it is important to noteBigDecimal B1 =NewBigDecimal ("1.301"); BigDecimal B2=NewBigDecimal ("101"); //BigDecimal B3 = b1.divide (B2);//if it's not divisible, there'll be an exception .BigDecimal B3 = b1.divide (b2,2, BIGDECIMAL.ROUND_HALF_UP); //The second parameter is the meaning of preserving two decimal places//The third parameter is the retention mode: the nearest number rounding (that is, rounding retention mode), and many other modesSYSTEM.OUT.PRINTLN (B3);//keep two bits and get 0.02 results    }    }

Java Learning Notes (math class, Arrays class, BigInteger class, BigDecimal Class)