Various practical classes

Practical class

Packaging class Construction

Conversion of basic data types to basic types

Method One

Boxing: Converting the basic data type to the corresponding object type

Role:

1. Make the necessary conversions when you need to use the object type data

For example, in a collection frame

2, the conversion is completed after the corresponding properties and methods, convenient operation

Public type (type value)

Integer intvalue = new integer (21);

Long longvalue = new Long (21L);

Character charvalue = new Character (' V ');

First Kind

Integer intvalue = new integer (21);//boxed data produces corresponding properties and methods

System.out.println (Intvalue);

int a = intvalue;//unboxing

System.out.println (a);

The second Kind

Integer integer = new Integer ("015");

System.out.println (integer);

int b = integer;

System.out.println (b);

Third Kind

Integer integer2 = integer. valueOf (23);//Boxing

System. out. println (INTEGER2);

int c = integer2.intvalue ();//Unpacking

System. out. println (c);

Fourth type

Integer integer3= 3;//Boxing

int d = Integer3; Unpacking

Conversion of string to base type

Convert strings to basic data types

int i5 = integer.parseint ("213");

SYSTEM.OUT.PRINTLN (i5);

float f = float.parsefloat ("123");

System.out.println (f);

Double I6 = double.parsedouble ("567");

System.out.println (I6);

Boolean i8 = Boolean.parseboolean ("0");

System.out.println (i8);

Basic data types are converted to string types

int i7 = 123;

String I9 = integer.tostring (i7);

System.out.println (I9);

The second Kind

String s = 123+ "";//Direct conversion

System. out. println (s);

Math class

provides two static constants E and PI

Math class

int num1 = Math. Max (23, 20);//Larger

System. out. println (NUM1);

double num2 = Math. POW (2, 3);//2 3-Time Square

System. out. println (num2);

double num3 = Math. sqrt (4);//Open square

System. out. println (NUM3);

int num4 = -6;//

int abs = Math. ABS (NUM4);//Absolute value

System. out. println (ABS);

double angle = (Math. PI/2);

double sin = Math. Sin (angle);//sine

System. out. println (sin);

double cos = Math. Cos (angle);//

System. out. println (COS);

double tan = Math. Tan (angle);

System. out. println (tan);

Double ASIN = Math. ASIN (angle);

Random method

Returns a random number from 0 to 1 (including 0 less than 1)

Outputs a random number from 1 to 10

int random = (int) (Math. Random() *10+1);

System. out. println (random);

Random

int random = (int) (Math. Random() *10+1);

System. out. println (random);

int check = Math. Random () >0.5?1:0;

System. out. println (check);

int random2 = (int) (Math. Random() *6+5);

System. out. println (RANDOM2);

Trim returns a copy of the string, ignoring leading and trailing blanks.

Substring intercept

IndexOf Find

Replace returns a new string, which is newChar obtained by replacing all occurrences of this string oldChar .

Replace (char OldChar, char Newchar)

Returns a new string that is obtained by replacing all OldChar that appear in this string with Newchar.

toUpperCase ()

Converts all characters in this String to uppercase using the rules of the default locale.

StringBuffer

Append (Boolean B) Appends the string representation of a Boolean parameter to the sequence.

Various practical classes