Common objects in Java--basic wrapper classes

For more operations on the basic data types, more convenient operation, Java provides the corresponding class type for each of the basic data types. Wrapper class Type:

BYTE byte

Short Short

int Integer

Long Long

float float

Double Double

Char Character

Boolean Boolean

Used for conversions between the base data type and the string.

Demo

public class Integerdemo { public static void Main (string[] args) { No, the trouble is coming. public static String tobinarystring (int i) System.out.println (integer.tobinarystring (100)); public static String tooctalstring (int i) System.out.println (integer.tooctalstring (100)); public static String tohexstring (int i) System.out.println (integer.tohexstring (100)); public static final int Max_value System.out.println (Integer.max_value); public static final int Min_value System.out.println (Integer.min_value); } }

how to construct an Integer:

public Integer (int value)

Public Integer (String s)

Note: This string must be made up of numeric characters

Demo

public class Integerdemo { public static void Main (string[] args) { Mode 1 int i = 100; Integer II = new Integer (i); System.out.println ("II:" + II); Mode 2 String s = "100"; NumberFormatException String s = "abc"; Integer III = new Integer (s); System.out.println ("III:" + III); } }

Mutual conversions of type int and String type:

INT--String

String.valueof (number)

String--INT

Integer.parseint (s)

Demo:

public class Integerdemo { public static void Main (string[] args) { INT--String int number = 100; Mode 1 String S1 = "" + number; System.out.println ("S1:" + S1); Mode 2 String s2 = string.valueof (number); System.out.println ("s2:" + s2); Mode 3 INT--Integer--String Integer i = new Integer (number); String s3 = i.ToString (); System.out.println ("S3:" + S3); Mode 4 public static String toString (int i) String S4 = integer.tostring (number); System.out.println ("S4:" + S4); System.out.println ("-----------------"); String--INT String s = "100"; Mode 1 String--Integer--INT Integer II = new Integer (s); public int intvalue () int x = Ii.intvalue (); System.out.println ("x:" + x); Mode 2 public static int parseint (String s) int y = Integer.parseint (s); System.out.println ("y:" +y); } }

operation of the binary conversion in Integer

Common basic binary conversions

public static String tobinarystring (int i)

public static String tooctalstring (int i)

public static String tohexstring (int i)

Decimal to another binary

public static String toString (int i,int radix)

by this, we also saw the range ofthe binary: 2-36

for what ? 0,... 9,a...z

Other binary to Decimal

public static int parseint (String s,int Radix)

Demo

public class Integerdemo { public static void Main (string[] args) { decimal to binary, octal, hex System.out.println (integer.tobinarystring (100)); System.out.println (integer.tooctalstring (100)); System.out.println (integer.tohexstring (100)); System.out.println ("-------------------------"); decimal to another binary System.out.println (integer.tostring (100, 10)); System.out.println (integer.tostring (100, 2)); System.out.println (integer.tostring (100, 8)); System.out.println (integer.tostring (100, 16)); System.out.println (integer.tostring (100, 5)); System.out.println (integer.tostring (100, 7)); System.out.println (integer.tostring (100,-7)); System.out.println (integer.tostring (100, 70)); System.out.println (integer.tostring (100, 1)); System.out.println (integer.tostring (100, 17)); System.out.println (integer.tostring (100, 32)); System.out.println (integer.tostring (100, 37)); System.out.println (integer.tostring (100, 36)); System.out.println ("-------------------------"); other binary to decimal System.out.println (Integer.parseint ("100", 10)); System.out.println (Integer.parseint ("100", 2)); System.out.println (Integer.parseint ("100", 8)); System.out.println (Integer.parseint ("100", 16)); System.out.println (Integer.parseint ("100", 23)); NumberFormatException System.out.println (Integer.parseint ("123", 2)); } }

new features of JDK5-Auto boxing / unpacking:

Auto-Boxing: Converting a base type to a wrapper class type

Auto-unpacking: Converting wrapper class types to basic types

Note A small problem:

when in use, Integer x = null; The code will appear NullPointerException.

It is recommended that you first determine whether it is null before youuse it.

Demo

public class Integerdemo { public static void Main (string[] args) { defines a wrapper class type variable I for an int type Integer i = new integer (100); Integer II = 100; II + = 200; System.out.println ("II:" + II); through the post-compilation code Integer II = integer.valueof (100); Automatic Boxing II = integer.valueof (Ii.intvalue () + 200); automatic unpacking and automatic packing System.out.println ((New StringBuilder ("II:")). Append (ii). toString ()); Integer III = NULL; NullPointerException if (iii! = NULL) { III + = 1000; SYSTEM.OUT.PRINTLN (iii); } } }

Integer data is directly assigned, and if between -128 and 127 , the data is fetched directly from the buffer pool:

Demo

public class Integerdemo { public static void Main (string[] args) { Integer i1 = new Integer (127); Integer i2 = new Integer (127); System.out.println (I1 = = I2); System.out.println (I1.equals (I2)); System.out.println ("-----------"); Integer i3 = new Integer (128); Integer i4 = new Integer (128); System.out.println (i3 = = I4); System.out.println (I3.equals (I4)); System.out.println ("-----------"); Integer i5 = 128; Integer I6 = 128; SYSTEM.OUT.PRINTLN (i5 = = I6); System.out.println (I5.equals (I6)); System.out.println ("-----------"); Integer i7 = 127; Integer i8 = 127; System.out.println (i7 = = i8); System.out.println (I7.equals (i8)); by looking at the source code, we know that for data between -128 and 127 , a data buffer pool is made, and if the data is within that range, no new space is created each time Integer II = integer.valueof (127); } }

Common objects in Java--basic wrapper classes