Sixth Chapter String

6 String

6.1, the characteristics of string

String s= "ABC"; s is a class-type variable, "ABC" is an object

Once the string is initialized, it cannot be changed.

String S1=new string ("abc");

What is the difference between S and S1:

S has an object in memory, S1 has two objects in memory

6.2 Common methods

1. Get

int length ();

char charAt (int index); Gets the character at that position, depending on the position

int indexOf (int ch); Gets the position of the first occurrence of the character in the string according to the CH character

int indexOf (int ch,int formindex); get the ch character where the string appears, starting at the Formindex specified position

int IndexOf (string s); Gets the position where the first occurrence of the string is based on s

int indexOf (String s,int formindex), starting at the Formindex specified position, get s where the string appears

Stringindexoutofboundsexception occurs when accessing a corner label that does not exist in a string

If not found, return-1

int Lasetindexof (); The position is reversed from the last position of the string, and the usage is the same as indexof.

2. Judgment

Boolean startwith (String str), whether the string starts with Str

Boolean endsWith (String str), whether the string ends with Str

Boolean isEmpty (); string is empty

Boolean contains (string str), whether the string contains str

Boolean equals (String str) to determine whether the string contents are the same

Boolean equalsignorecase (String str), ignoring case to determine if string is the same

3. Conversion

The character array is converted to a string:

Constructor: String (char[])

String (Char[],offset,count) converts a portion of a character array into a string

Static methods: Static String copyvalueof (char[] data);

Static String copyvalueof (char[] data,int offset,int count);

The byte array is converted to a string:

Constructor: String (byte[])

String (Byte[],offset,count) converts a portion of a character array into a string

The basic data class turns into a string:

static String valueOf (int);

Static String valueOf (double);

The string is converted to a character array/byte array:

Char[] ToCharArray ();

Byte[] GetBytes ();

4. Replace

String replace (Oldchar,newchar);

If the character to be replaced does not exist, the original string is returned

String replace (OLDSTR,NEWSTR);

5. Cutting

String[] Split (regex);

6, sub-string

String substring (begin);

String substring (begin,end), containing the header, not including the tail

Get part of a string

7. Conversion

String toUpperCase (); String toLowerCase (); strings are converted to uppercase or lowercase

string trim (); Remove spaces at both ends of the string

int CompareTo (string), a natural order comparison of two strings

6.3 StringBuffer

StringBuffer is a container that is variable in length and can be modified for the contents of a string

1. Insert and delete

StringBuffer append (); Add the data as a parameter to the end of the existing data

StringBuffer Insert (index,data); You can add data to the specified location

StringBuffer Delete (int start,int end); Delete data containing start does not contain end

StringBuffer deletecharat (int index); Delete the character at the specified position

2. Get the location of the string:

int indexOf (String s);

int lastIndexOf (String s);

int length ();

3. Positioning

char charAt (int index); Gets the character at the specified position:

StringBuffer replace (int start,int end,string s), from start position to end position, replaced by s

void Setcharat (int index,char ch); Sets the character at the specified position

4. After the JDK version 1.5, StringBuilder appeared.

StringBuffer is thread synchronization

StringBuilder is thread not synchronizing

6.4 Basic data type Object wrapper class

Basic data wrapper class

BYTE byte

Short Short

Long Long

int Integer

Boolean Boolean

float float

Double Double

Char Character

1, the most common role:

Conversions between basic data types and strings

2. The basic data type is converted into a string

Basic data type + "";

Wrapper class. toString (base data type value);

such as: Integer.tostring (36);//Change 36 to "36"

3. String converted to basic data type

Static wrapper class. Parse basic data type (String s);

Object. Basic data Type value ();

6.5 Decimal and other binary reciprocal transfers

1, decimal into other binary

Tobinarystring (); Turn binary

Tohexstring (); turn octal

Tooctalstring (); Turn hex

2. Convert other binary into decimal

parseint (String,radix);

6.6 New Features

Integer x = 4; auto-boxing, 4 equals new Integer (4)

x = x +2; automatically unpacking, after the operation of the x into the int type, the box is assigned to X

Integer m = 128;

Integer n = 128;

m==n;//result bit false

Integer a = 127;

Integer B = 127;

The a==b;//result is true because A and B point to the same integer object. When the value is within the byte range, if the value already exists, no new space will be opened.

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Sixth Chapter String