Java Learning Summary II

Trigonometric Methods

Math.sin (radians): Math.sin (MATH.PI/6) =0.5

Math.Cos (radians): Math.Cos (MATH.PI/3) =0.5

Math.tan (radians): Math.tan (MATH.PI/3) =1.732

Math.toradians (degrees): Math.toradians (+) =math.pi/6=0.5236

Math.todegrees (radians): Math.todegrees (MATH.PI/2) =90.0

Math.asin (a): Math.asin (0.5) =math.pi/6=0.52359877

Math.acos (a): Math.acos (0.5) =math.pi/3=1.0471975511965979

Math.atan (a): Math.atan (1.0) =math.pi/4=0.7853981633974483

exponential function Method

Math.exp (1) =math.e=2.718281828459045

Math.log (MATH.E) =1.0

MATH.LOG10 (10) =1.0

Math.pow (2,3) =8.0

MATH.SQRT (4) =2.0

Rounding Function Method

Math.ceil (x): Math.ceil (4.4) =5.0 or Math.ceil (4.6) =5.0

Math.floor (x): Math.floor (4.4) =4.0 or Math.floor (4.6) =4.0

Math.Round (x): rounded that is math.round (4.4) =4 or Math.Round (4.6) =5

Math.rint (x): Returns the nearest integer if the distance is equal to the nearest even number. Math.rint (4.4) =4.0 or math. (4.5) =4.0 (even) or Math.rint (4.6) =5.0

min, Max and ABS methods

Math.min (2,4) return 2,math.min (2,4.0) return 2.0

Math.max (2,3) return 3,math.max (2.0,3) return 3.0

Math.Abs (-2) return 2,math.abs (-2.0) return 2.0

Random Method

0.0<=math.random () <1.0

(int) (Math.random () *10) returns a random integer between 0~9

50+ (int) (Math.random () *50) returns a random integer between 50~99

50.0<=50+math.random () *50<100

Character class method

Character.isdigit (' 0~9 ') returns Ture,character.isdigit (' a ') returns false or Charcter.isdigit (' a ') returns false

Character.isletter (' a ') returns True,character.isletter (' a ') return True,character.isletter (' 9 ') returns false

Character.isletterordigit (' a ') returns True,character.isletterordigit (' a ') returns True,character.isletterordigit (' 0~9 ') Returns True

Character.islowercase (' a ') returns True,character.islowercase (' a ') return False,character.islowercase (' 8 ') returns false

Character.isuppercase (' a ') returns True,character.isuppercase (' a ') return False,character.isuppercase (' 8 ') returns false

Character.tolowercase (' a ') returns A,character.tolowercase (' a ') returns A,character.tolowercase (' 8 ') return 8

Character.touppercase (' a ') returns A,character.touppercase (' a ') return A,character.touppercase (' @ ') return @

simple methods for string objects

"String". Length () returns the number of characters in a string

"String". CharAt (index) returns the character at the specified position in the string (index starts at 0)

"String A". Concat ("string B") returns "string a string B"

"String". toLowerCase () returns "String lowercase"

"String". toUpperCase () returns "String uppercase"

"String". Trim () Returns a new "string" that removes whitespace characters from both sides, including whitespace, \ t, \f, \ r, \ n

System.out.println ("Good Good study,

Day up! "); Statement error, string constants cannot be serialized, serial must be added ' + '

comparison method for string objects

"A". Equals ("a") returns True, "a". Equals ("B") returns false

"A". Equalsignorecase ("a") returns True, "a". Equalsignorecase ("B") returns false

"A". CompareTo ("B") returns 1, "B". CompareTo ("A") returns 1, "a". CompareTo ("a") returns 0, "a". CompareTo ("a") returns-32

"A". Comparetoignorecase ("a") returns 0, "a". Comparetoignorecase ("B") returns-1, "B". CompareTo ("A") returns 1

"AB". StartsWith ("A") returns True, "AB". StartsWith ("") returns True, "AB". StartsWith ("B") returns false, "AB". StartsWith ("AB") returns false

"AB". EndsWith ("B") returns True, "AB". EndsWith ("") returns True, "AB". EndsWith ("A") returns false, "AB". EndsWith ("AB") returns false

"ABC". CONTAINS ("AB") returns True, "ABC". CONTAINS ("BC") returns True, "ABC". CONTAINS ("AC") returns FALSE, "ABC". CONTAINS ("") returns True

methods for string objects to get substrings

"ABCD efgh ijkl". Substring (5) return to "Efgh IJKL"

"ABCD efgh ijkl". substring (5,9) return "EFGH"

String object method that gets the index value of the character in the string

INDEXOF (CH): Returns the subscript of the first ch that appears in a string, if not, returns 1

IndexOf (Ch,fromindex): Returns the subscript of the first CH that appears after the string fromIndex, if not, returns 1

IndexOf (s): Returns the subscript of the first string s that appears in the string, or 1 if not

IndexOf (S,fromindex): Returns the subscript of the first string s that appears after fromIndex in a string, if not, returns 1

LASTINDEXOF (CH): Returns the subscript of the last ch that appears in the string, if not, returns 1

LastIndexOf (Ch,fromindex): Returns the subscript of the last ch that occurred before the string fromIndex, if not, returns-1

LastIndexOf (s): Returns the subscript of the last string that appears in the string, if not, returns 1

LastIndexOf (S,fromindex): Returns the subscript of the last string s that appears before fromIndex in the string, if not, returns 1

Suppose a string s contains a first and last name separated by a space, and the following code can be used to extract the first and last names:

int k = S.indexof ("");

String firstName = s.substring (0,k);

String lastName = s.substring (k+1);

the conversion between a string and a number

int intvalue = Integer.parseint ("123");

D ouble doublevalue = double.parsedouble ("123.456");

String s = 123+ ""; System.out.println (s); the output is a string 123

System.out.println ("Welcome" + (' \u0001 ' + 1)) outputs the result of Welcome 2

System.out.println ("Welcome" +1+1) outputs the result of Welcome 11

System.out.println ("Welcome" + ' a ' + 1) outputs a result of Welcome A1

System.out.println (' A ' +1+ "Welcome") outputs the result of 98 Welcome

methods for scanner objects

Java.util.Scanner input = new Java.util.Scanner (system.in);

Input.next () reads the string ending with a white space character (' ', ' \ t ', ' \f ', ' \ n ', ' \ R ')

Input.nextline () reads a string that presses the ENTER key to the end flag

For example:

Java.util.Scanner input = new Java.util.Scanner (system.in);

System.out.print ("Enter three words separated by spaces:");

String S1 = Input.next ();

String s2 = Input.next ();

String s3 = Input.next ();

System.out.println (S1);

SYSTEM.OUT.PRINTLN (S2);

System.out.println (S3);

Displays:

Enter three words separated by Spaces:welcome to Java

Welcome

To

Java

For example:

Java.util.Scanner input = new Java.util.Scanner (system.in);

System.out.print ("Enter a Line:");

String s = input.nextline ();

SYSTEM.OUT.PRINTLN ("The line entered is" +s);

Displays:

Enter a line:welcome to Java

The line entered are Welcome to Java

To avoid input errors, do not use Nextfloat () after Nextbyte (), Nextshort, Nextint (), Nextlong (), nextdouble (), nextline (), and Next ()

Java Learning Summary II