Detailed analysis of String class in Java

Strings are widely used in Java programming. Strings are objects in Java. Java provides the String class to create and operate strings. This article will introduce the contents of the String class in detail.

Create a string

The simplest way to create a string is as follows:

String greeting = "php Chinese website";

Encountered in the code When it is a string constant, the value here is "php中文网"", and the compiler will use this value to create a String object.

Like other objects, you can use keywords and constructs Method to create a String object.

The String class has 11 construction methods, which provide different parameters to initialize the string, such as providing a character array parameter:

StringDemo.java file code:

public class StringDemo{
 public static void main(String args[]){
  char[] helloArray = { 'p', 'h', 'p'}; 
  String helloString = new String(helloArray);
   System.out.println( helloString ); 
   } 
   }

The compilation and running results of the above example are as follows:

php

Note: String class is immutable, so once you create a String object, its value cannot be changed Changed (see the notes section for details).

If you need to make a lot of modifications to the string, you should choose to use the StringBuffer & StringBuilder class.

String length

Use Methods for obtaining information about an object are called accessor methods.

One accessor method of the String class is the length() method, which returns the number of characters contained in the string object.

The following After the code is executed, the len variable is equal to 14:

StringDemo.java file code:

public class StringDemo {
 public static void main(String args[])
  { 
  String site = "www.php.cn"; 
  int len = site.length(); 
  System.out.println( "php中文网网址长度 : " + len ); 
  } 
}

The compilation and running results of the above example are as follows:

php中文网网址 : 14

Connection string

String class provides a method to concatenate two strings:

string1.concat(string2);

Return string2 to connect string1 to a new string. You can also use concat for string constants () method, such as:

"我的名字是 ".concat("php");

More commonly used is to use the ' ' operator to connect strings, such as:

"Hello," + " php" + "!"

The result is as follows:

"Hello, runoob!"

The following is an example :

StringDemo.java file code:

public class StringDemo {
 public static void main(String args[])
  {
   String string1 = "php中文网网址："; 
   System.out.println("1、" + string1 + "www.php.cn"); 
   } 
}

The compilation and running results of the above example are as follows:

1、php中文网网址：www.php.cn

Create formatted string

We know the output formatting Numbers can use the printf() and format() methods.

The String class uses the static method format() to return a String object instead of a PrintStream object.

The static method format() of the String class can Used to create reusable formatted strings, not just for one-time printout.

As shown below:

System.out.printf("浮点型变量的值为 " + "%f, 整型变量的值为 " + " %d, 字符串变量的值为 " + "is %s", floatVar, intVar, stringVar);

You can also write like this

String fs; fs = String.format("浮点型变量的值为 " + "%f, 整型变量的值为 " + " %d, 字符串变量的值为 " + " %s", floatVar, intVar, stringVar)

String method

The following are the methods supported by the String class. For more details, see Java String API Documentation:

##1char charAt(int index)2int compareTo(Object o)3int compareTo(String anotherString)4int compareToIgnoreCase(String str)5String concat(String str)6boolean contentEquals(StringBuffer sb)7static String copyValueOf(char[] data)8static String copyValueOf(char[] data, int offset, int count)9boolean endsWith(String suffix)10boolean equals(Object anObject)11boolean equalsIgnoreCase(String anotherString)12byte[] getBytes()13byte[] getBytes(String charsetName)14void getChars(int srcBegin, int srcEnd, char[] dst, int dstBegin)15int hashCode()16int indexOf(int ch)17int indexOf(int ch, int fromIndex)18int indexOf(String str)19int indexOf(String str, int fromIndex)20String intern()21int lastIndexOf(int ch)22int lastIndexOf(int ch, int fromIndex)23int lastIndexOf(String str)24int lastIndexOf(String str, int fromIndex)25int length()26boolean matches(String regex)27boolean regionMatches(boolean ignoreCase, int toffset, String other, int ooffset, int len)28boolean regionMatches(int toffset, String other, int ooffset, int len)29String replace(char oldChar, char newChar)30String replaceAll(String regex, String replacement)31String replaceFirst(String regex, String replacement)32String[] split(String regex)33String[] split(String regex, int limit)34boolean startsWith(String prefix)

SN(serial number)	Method description
	Returns the char value at the specified index.
	Compare this string to another object.
	Compares two strings lexicographically.
	Compares two strings lexicographically, regardless of case.
	Concatenates the specified string to the end of this string.
	Returns true if and only if the string has the same order of characters as the specified StringBuffer.
	Returns a String representing this sequence of characters in the specified array.
	Returns a String representing this sequence of characters in the specified array.
	Tests whether this string ends with the specified suffix.
	Compares this string to the specified object.
	Compares this String to another String, regardless of case.
	Encode this String into a sequence of bytes using the platform's default character set, and store the result in a new byte array.
	Encodes this String into a sequence of bytes using the specified character set and stores the result in a new byte array.
	Copies characters from this string to a target character array.
	Returns the hash code of this string.
	Returns the index of the first occurrence of the specified character in this string.
	Returns the index of the first occurrence of the specified character in this string, starting the search at the specified index.
	Returns the index of the first occurrence of the specified substring in this string.
	Returns the index of the first occurrence of the specified substring in this string, starting at the specified index.
	Returns the canonical representation of a string object.
	Returns the index of the last occurrence of the specified character in this string.
	Returns the index of the last occurrence of the specified character in this string, starting from the specified index and performing a reverse search.
	Returns the index of the rightmost occurrence of the specified substring in this string.
	Returns the index of the last occurrence of the specified substring in this string, starting the reverse search from the specified index.
	Returns the length of this string.
	Tells whether this string matches the given regular expression.
	Tests whether two string ranges are equal.
	Tests whether two string ranges are equal.
	Returns a new string obtained by replacing all occurrences of oldChar with newChar.
	Replaces all substrings of this string that match the given regular expression with the given replacement.
	Replaces the first substring of this string matching the given regular expression with the given replacement.
	Splits this string based on matches of the given regular expression.
	Split this string based on matching the given regular expression.
	Tests whether this string starts with the specified prefix.
35	boolean startsWith(String prefix, int toffset) Tests whether the substring of this string starting at the specified index begins with the specified prefix.
36	CharSequence subSequence(int beginIndex, int endIndex) Returns a new character sequence that is a subsequence of this sequence.
37	String substring(int beginIndex) Returns a new string that is a substring of this string.
38	String substring(int beginIndex, int endIndex) Returns a new string that is a substring of this string.
39	char[] toCharArray() Convert this string to a new character array.
40	String toLowerCase() Converts all characters in this String to lowercase using the rules of the default locale.
41	String toLowerCase(Locale locale) Converts all characters in this String to lowercase using the rules of the given Locale.
42	String toString() Returns this object itself (it's already a string!).
43	String toUpperCase() Converts all characters in this String to uppercase using the rules of the default locale.
44	String toUpperCase(Locale locale) Converts all characters in this String to uppercase using the rules of the given Locale.
45	String trim() Returns a copy of the string, ignoring leading and trailing whitespace.
46	static String valueOf(primitive data type x)               Returns the string representation of the x parameter of the given data type.

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