Java Learning Note (String Class)

String stands for strings, and in Java all string literals are implemented as instances of this class

Character of the string and simple analysis of the principle:

 Packagedemo;/** Features of the String class: * All "" is a String object * Once created is a constant, cannot be changed*/ Public classStringdemo { Public Static voidMain (string[] args) {//Discovery created object does not require newString str = "ABCD";        System.out.println (str); //output: ABCD instead of memory address because the string class overrides the ToString methodstr = "EFGH";        System.out.println (str); //output: Efgh, didn't it say that constants don't change? Here's why://The string itself is an object, in heap memory, where the string essence is an array of characters//Source: Private final char value[]; there is a final modification, so string is a constant//str = "EFGH" is reopened in memory, the direction of STR has changed, and the "ABCD" string object has not changed            }}

How the String class is created and compared:

 Packagedemo; Public classStringdemo { Public Static voidMain (string[] args) {//The string is defined in two ways, direct =, using the construction method of stringString str1 =NewString ("ABC"); String str2= "ABC"; //Direct = more convenient, but there are differencesSystem.out.println (str1==STR2);//falseSystem.out.println (Str1.equals (str2));//true//use the construction method to define the principle://two objects are actually created, one is a new string object, and the other is an "ABC" Object//The new string object holds the address of the character array object "ABC".//str1 pointing to the new string object//when printing str1, call the overridden ToString method to find the string//because the "ABC" Object already exists//so str2 directly points to the "ABC" object and does not create a new object//Therefore, STR1==STR2 is false because the address of the object is different//while Str1.equals (STR2) is true, the principle://The string class inherits object, overrides the parent class method equals, and establishes the string's own string comparison method//that is, as long as each character of the string is true, regardless of the address    }}

How to construct the String class:

1. Official information: string (byte[] byte) constructs a new string by decoding the specified byte array using the platform's default character set

Example:

 Packagedemo;/** Construction method of the string class*/ Public classStringDemo2 { Public Static voidMain (string[] args) {byte[] bytes = {97,98,99,100}; String s=NewString (bytes);        System.out.println (s); //output: ABCD//The result of querying the encoded table for each byte in the byte array    }}

2. Official information: String (byte[] byte, int offset, int length)

Example:

 Packagedemo;/** Construction method of the string class*/ Public classStringDemo2 { Public Static voidMain (string[] args) {byte[] bytes = {65,66,67,68,69}; String s=NewString (Bytes, 2, 3); //The second argument is the starting index, and the third parameter is the number of selectionsSystem.out.println (s); //Output: CDE    }}

3. Official information: string (char[] value) assigns a new string that represents the sequence of characters currently contained in the character array parameter

Example:

 Packagedemo;/** Construction method of the string class*/ Public classStringDemo2 { Public Static voidMain (string[] args) {function (); }     Public Static voidfunction () {Char[] ch = {' A ', ' B ', ' C ', ' d ', ' e '}; String s=NewString (CH);    System.out.println (s); }}//Output: ABCDE

4. Similar to the first two, official information: String (char[] value, int offset, int length)

Example:

 Packagedemo;/** Construction method of the string class*/ Public classStringDemo2 { Public Static voidMain (string[] args) {function (); }     Public Static voidfunction () {Char[] ch = {' A ', ' B ', ' C ', ' d ', ' e '}; String s=NewString (ch,1,3);    System.out.println (s); }}//Output: BCD

There are a lot of construction methods, but these are often

Other methods of the string class:

1. Official Information: int length () returns the length of this string (relatively simple, no example)

2. Official information: string substring (int beginindex) returns a new string that is a substring of this string

Another: String substring (int beginindex,int endIndex) Ibid., one more end index value

Example:

 Packagedemo; Public classStringDemo2 { Public Static voidMain (string[] args) {function (); }     Public Static voidfunction () {String str= "Iamhandsome"; String str1= Str.substring (3); String str2= Str.substring (3, 5);        System.out.println (STR1);    System.out.println (STR2); }}/*output: Handsomeha Note here that the interval is left closed to the right, meaning to include the starting index, not including the terminating index*/

3. Official Information: Boolean startsWith (String prefix)

Tests whether a string starts with the specified prefix

There should also be suffixes with prefixes:

Boolean endwith (String suffix)

4. Official Information: Boolean contains (string s) to determine if a string contains another string

5.int indexOf (char ch) finds the first occurrence of a character in a string index

3,4,5 Example:

 Packagedemo; Public classStringDemo2 { Public Static voidMain (string[] args) {function (); }     Public Static voidfunction () {string string= "Iamhandsome"; Booleanb = String.startswith ("Ia"); System.out.println (b);//true        BooleanB1 = String.endswith ("ome"); System.out.println (B1);//true        BooleanB2 = String.contains ("Hand"); System.out.println (B2);//true        intA = String.IndexOf ("a"); System.out.println (a);//1    }}

6. Turn the string into a byte array:

Byte[] GetBytes ()

This feature is constructed in the opposite way as String

Example:

 Packagedemo; Public classStringDemo2 { Public Static voidMain (string[] args) {function (); }     Public Static voidfunction () {String str= "ABC"; byte[] bytes =str.getbytes ();  for(inti=0; i<bytes.length; i++) {System.out.println (bytes[i]); }    }}/*Output: 979899*/

7. Convert the string to a character array: char[] ToCharArray ();

 Packagedemo; Public classStringDemo2 { Public Static voidMain (string[] args) {function (); }     Public Static voidfunction () {String str= "ABC"; Char[] chars =Str.tochararray ();  for(inti=0; i<chars.length; i++) {System.out.println (chars[i]); }    }}/*output: ABC*/

Compare strings if they are identical

Example:

 Packagedemo; Public classStringDemo2 { Public Static voidMain (string[] args) {function (); }     Public Static voidfunction () {String str1= "ABC"; String str2= "ABC"; Booleanb1=str1.equals (STR2); BooleanB2 =str1.equalsignorecase (STR2); System.out.println (B1);//falseSystem.out.println (B2);//true//compare strings are the same, the second ignores case    }}

Java Learning Note (String Class)