Java String Class

Strings are widely used in Java programming. In Java, strings are objects. Java provides the String class to create and manipulate strings.

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Creating Strings

The simplest way to create a string is as follows:

When a string constant is encountered in code, the value here is "Example", the compiler will use that value to create a String object.

Like other objects, you can use the keyword and constructor methods to create String objects.

Creating strings with constructors:

Strings created with String are stored in the public pool, while string objects created with new are on the heap:

The String class has 11 constructors. These methods provide different parameters to initialize strings, for example, providing a character array parameter:

The compilation and execution result of the above example is as follows:

example

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

If you need to make many modifications to a string, you should choose to useStringBuffer & StringBuilder classes。

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String Length

Methods used to obtain information about an object are called accessor methods.

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

After executing the following code, the len variable equals 14:

The compilation and execution result of the above example is as follows:

Example网址长度 : 14

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Concatenating Strings

The String class provides a method to concatenate two strings:

Returns a new string that is string2 concatenated with string1. You can also use the concat() method on string literals, such as:

"我的名字是 ".concat("Example");

More commonly, the '+' operator is used to concatenate strings, such as:

"Hello," + " example" + "!"

The result is as follows:

"Hello, example!"

Here is an example:

The compilation and execution result of the above example is as follows:

1、Example网址：www.example.com

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Creating Formatted Strings

We know that printf() and format() methods can be used for formatted output of numbers.

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

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

As shown below:

You can also write it like this

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String Methods

Below are the methods supported by the String class. For more details, seeJava String APIdocumentation:

SN (Serial Number)	Method Description
1	char charAt(int index) Returns the char value at the specified index.
2	int compareTo(Object o) Compares this string to another object.
3	int compareTo(String anotherString) Compares two strings lexicographically.
4	int compareToIgnoreCase(String str) Compares two strings lexicographically, ignoring case.
5	String concat(String str) Concatenates the specified string to the end of this string.
6	boolean contentEquals(StringBuffer sb) Returns true if and only if this string has the same character sequence as the specified StringBuffer.
7	static String copyValueOf(char[] data) Returns a String representing the character sequence in the specified array.
8	static String copyValueOf(char[] data, int offset, int count) Returns a String representing the character sequence in the specified array.
9	boolean endsWith(String suffix) Tests whether this string ends with the specified suffix.
10	boolean equals(Object anObject) Compares this string to the specified object.
11	boolean equalsIgnoreCase(String anotherString) Compares this String to another String, ignoring case.
12	byte[] getBytes() Encodes this String into a byte sequence using the platform's default charset, and stores the result into a new byte array.
13	byte[] getBytes(String charsetName) Encodes this String into a byte sequence using the specified charset, and stores the result into a new byte array.
14	void getChars(int srcBegin, int srcEnd, char[] dst, int dstBegin) Copies characters from this string into the destination character array.
15	int hashCode() Returns the hash code of this string.
16	int indexOf(int ch) Returns the index of the first occurrence of the specified character in this string.
17	int indexOf(int ch, int fromIndex) Returns the index of the first occurrence of the specified character in this string, searching from the specified index.
18	int indexOf(String str) Returns the index of the first occurrence of the specified substring in this string.
19	int indexOf(String str, int fromIndex) Returns the index of the first occurrence of the specified substring in this string, starting from the specified index.
20	String intern() Returns the canonical representation of the string object.
21	int lastIndexOf(int ch) Returns the index of the last occurrence of the specified character in this string.
22	int lastIndexOf(int ch, int fromIndex) Returns the index of the last occurrence of the specified character in this string, searching backward from the specified index.
23	int lastIndexOf(String str) Returns the index of the rightmost occurrence of the specified substring in this string.
24	int lastIndexOf(String str, int fromIndex) Returns the index of the last occurrence of the specified substring in this string, searching backward from the specified index.
25	int length() Returns the length of this string.
26	boolean matches(String regex) Tells whether this string matches the given regular expression.
27	boolean regionMatches(boolean ignoreCase, int toffset, String other, int ooffset, int len) Tests whether two string regions are equal.
28	boolean regionMatches(int toffset, String other, int ooffset, int len) Tests whether two string regions are equal.
29	String replace(char oldChar, char newChar) Returns a new string resulting from replacing all occurrences of oldChar in this string with newChar.
30	String replaceAll(String regex, String replacement) Replaces each substring of this string that matches the given regular expression with the given replacement.
31	String replaceFirst(String regex, String replacement) Replaces the first substring of this string that matches the given regular expression with the given replacement.
32	String[] split(String regex) Splits this string around matches of the given regular expression.
33	String[] split(String regex, int limit) Splits this string around matches of the given regular expression.
34	boolean startsWith(String prefix) Tests whether this string starts with the specified prefix.
35	boolean startsWith(String prefix, int toffset) Tests whether the substring of this string beginning at the specified index starts 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() Converts 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 the object itself (it is 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.
47	contains(CharSequence chars) Determines whether it contains the specified character sequence.
48	isEmpty() Determines whether the string is empty.

Other Extensions