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This article mainly explains "how to convert big data string". The content of the explanation in the article is simple and clear, and it is easy to learn and understand. Please follow the editor's train of thought slowly and deeply. Let's study and learn "how to convert big data string"!

Immutable string:-String. The string itself cannot be changed, regardless of the reference to the string.

String S1 = "1000phone"

Variable string:-StringBuilder/StringBuffer. The string itself can change, regardless of references to mutable strings

StringBuffer sBuffer = new StringBuffer ("1000phone")

The immutable string itself is a constant, stored in the constant area and stored in a special area in the heap area.

Characteristics of string constants: only one string constant is allowed to be stored in the constant area.

String s = "1000phone"; / / immutable string

When executing s, it will go to the constant area to find a string called 1000phone. If there is a direct request for s to save his address, if not, it will open up a space to store 1000phone in the constant area.

String S3 = new String ("1000phone")

When executing S3, because of the new, there must be a space in the heap now, and the 1000phone is passed to the object as a parameter. Saved in a String of the object

Using equals to compare String

two。 Conversion:

Convert a character array to a string

Char [] arr = {'pause, pause, clue, chop, roll, chop, chew, chew

String string1 = new String (arr); / / string1 = phone

Convert a string to a character array

Char [] arr1 = string.toCharArray ()

System.out.println (arr1)

Convert a byte array to a string

/ / String (byte [] bytes)

/ / String (byte [] bytes, int offset, int length)

/ / String (byte [] bytes, String charsetName) / / converts an array of bytes into characters using the specified encoding

Byte [] bytes = {97199899100}

String string3 = new String (bytes)

System.out.println (string3); / / abcd

Convert a string to a byte array

/ / byte [] getBytes ()

Byte [] bytes1 = string3.getBytes ()

Convert basic data types to strings

/ / String.valueOf ()

String string4 = String.valueOf (true)

System.out.println (string4); / / true

Substring:

/ / contains the start position, excluding the end position, to the first bit of the end position

String substring (int beginIndex, int endIndex)

Case conversion

String toLowerCase (); / / convert to lowercase

String toUpperCase (); / / convert to uppercase

Compare two strings in dictionary order

Dictionary order: compare the current two characters according to the ASCII table, and the larger ASCII code is considered to be the big character.

Rule: compare from the first character on the left

If the current character is different, the string with large ASCII is considered to be large, and the following characters stop comparing.

Specific rules for current character comparison: use the preceding character-the following character, to return the difference. If it is a negative number, the preceding string is less than the latter. On the contrary, the front one is big.

If the current character is the same, compare the second character and push it back in turn. If the character is the same in the end, the two strings are considered to be equal, and the difference returns 0.

"1000PHone" .compareto ("1000PHone"); / / 0

"1000AHone" .compareto ("1000BHone"); / /-1

"100000" .compareto ("100th"); / /-3

Variable string:

String buffer .StringBuffer / StringBuilder

Difference:

StringBuffer: appears in jdk1.0, is thread-safe, taking into account thread safety issues

StringBuilder: when it appears in jdk1.5, it is not thread safe and thread safety issues are not considered.

Note: when not considering thread safety, try to use StringBuilder because of its high speed and efficiency

Use:

StringBuffer sBuffer = new StringBuffer ()

/ / 1. Storage:

/ / StringBuffer append (boolean b) insert from last

SBuffer.append ("abcd"); / / abcd

/ / StringBuffer insert (int offset, boolean b) insert from the specified location

SBuffer.insert (4123)

System.out.println (sBuffer); / / abcd123

/ / 2. Delete:

/ / StringBuffer delete (int start, int end) delete part of the string

/ / StringBuffer deleteCharAt (int index) Delete a character

System.out.println (sBuffer.deleteCharAt (4)); / / abcd23

System.out.println (sBuffer.delete (2) 4); / / ab23

/ / 3. Modify:

/ / StringBuffer replace (int start, int end, String str) replaces the specified substring

/ / void setCharAt (int index, char ch) modifies one character

SBuffer.replace (1,3, "ab"); / / aab3

/ / 4. Get:

/ / char charAt (int index)

System.out.println (sBuffer.charAt (0)); / / a

/ / returns the subscript of the specified substring from left to right

/ / int indexOf (String str)

System.out.println (sBuffer.indexOf ("ab")) / / 1

/ / returns the index of the first occurrence of the specified substring in this string, starting with the specified index.

System.out.println (sBuffer.indexOf ("ab", 0); / / 1

System.out.println (sBuffer.indexOf ("ab", 2); / /-1

/ / int lastIndexOf (String str)

/ / returns the index of the specified substring (counting from the right) when this string first appears

System.out.println (sBuffer.indexOf ("ba")); / /-1

System.out.println (sBuffer.indexOf ("ab")) / / 1

/ / int lastIndexOf (String str, int fromIndex)

/ returns the index of the last occurrence of the specified character in this string, starting at the specified index.

System.out.println (sBuffer.indexOf ("ab", 1); / / 1

/ / 5. Reverse:

/ / StringBuffer reverse ()

System.out.println (sBuffer.reverse ()); / / 3baa

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