Important Java17 String

Strings are widely used in Java programming, where strings belong to objects, and Java provides a string class to create and manipulate strings.

Create a string

The simplest way to create a string is for example the following:

String greeting = "Hello world!";

When you encounter a string constant in your code, the value here is "Hello world!", which the compiler uses to create a string object.

Like other objects, you can use keyword and construction methods to create a string object.

The string class has 11 constructor methods that provide different parameters for initializing a string, such as providing a character array parameter:

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

The above example compiles execution results such as the following:

hello.

Note: The string class is a final class that cannot be changed , so once you create a string object, its value cannot be changed. If you need to make a lot of changes to a string, you should choose to use the StringBuffer & StringBuilder class.

Frequent usage

• char charAt (int index) returns the char value at the specified index.
• static string copyvalueof (char[] data) returns a string representing the sequence of characters in the specified array.
• Boolean endsWith (string suffix) tests whether this string ends with the specified suffix.
• Boolean Equals (object AnObject) to compare this string to the specified object.
• The Boolean equalsignorecase (string anotherstring) Compare this string to another string, regardless of uppercase or lowercase.
• Byte[] GetBytes () encodes this String into a byte sequence using the platform's default character set and stores the result in a new byte array.
• Byte[] GetBytes (string charsetname) encodes this String into a byte sequence using the specified character set and stores the result in a new byte array.
• int indexOf (int ch) returns the index of the specified character at the first occurrence of this string.
• int indexOf (int ch, int fromIndex) returns the index at the first occurrence of the specified character in this string, starting with the specified index.
• int indexOf (String str) returns the index where the specified substring first appears in this string.
• int lastIndexOf (int ch) returns the index of the specified character at the last occurrence in this string.
• int length () returns the length of this string.
• A Boolean matches (string regex) tells whether this string matches a given regular table.
• String replace (char OldChar, char Newchar) returns a new string that is obtained by replacing all OldChar that appear in this string with Newchar.
• String ReplaceAll (string regex, string replacement replaces this string with the given replacement to match all substrings of the given regular table.
• String[] Split (string regex) splits this string based on a match of the given regular table.
• String[] Split (string regex, int limit) splits this string by matching a given regular table.
• Boolean startsWith (string prefix) tests whether this string starts with the specified prefix.
• string substring (int beginindex) returns a new string that is a substring of this string.
• string substring (int beginindex, int endIndex) returns a new string that is a substring of this string.
• String toLowerCase () converts all characters in this string to lowercase using the rules of the default locale.
• String toUpperCase () converts all characters in this string to uppercase using the default locale's rules.
• String Trim () returns a copy of the string, ignoring leading and trailing blanks.
• The static string format (String format,object ... args) returns a formatted string using the specified format string and parameters.

Common topics (using JUnit demos)

@Testpublic void Testequels () {String test = "12345";    String test1 = "12345";    String test2 = new String ("12345");    String test3 = new String ("12345");    String t1 = test;    String t2 = "12" + "345";    Asserttrue (TEST==TEST1);    Asserttrue (TEST==T1);    Asserttrue (TEST==T2);    Asserttrue (TEST!=TEST2);       Asserttrue (TEST2!=TEST3);            } @Testpublic void Testnotchange () {String instring = "123";    String outstring = stubchangestring (instring);    Assertequals ("123", instring); Assertequals ("123test", outstring);}    private string Stubchangestring (String instring) {instring + = "Test"; return instring;}    @Testpublic void Testsubstring () {String test = "12345"; Assertequals ("2345", test.substring (1));}    @Testpublic void Testtoarrays () {list<string> ids = new arraylist<> ();    Ids.add ("1");    Ids.add ("2");    Ids.add ("3");    string[] id = ids.toarray (new string[0]);    Assertequals (3, id.length); Assertequals ("1", id[0]);}

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Important Java17 String