Java string type in the detailed

character of the string
A: Once the string is assigned, it cannot be changed.
Note: This refers to the contents of the string cannot be changed, not the reference cannot be changed.

B: Literals As String objects and different objects created by constructing methods

string s = new string ("Hello") and string s = "Hello";
the former creates 2 objects, which create 1 objects. The string literal is an object, with new superfluous.

= =: Compare the reference type comparison is the address value is the same
equals: Comparing reference types By default is also the same as comparing address values, and the string class overrides the Equals () method to compare whether the content is the same

<span style= "FONT-SIZE:18PX;" >public class StringDemo2 {public static void main (string[] args) {string S1 = new String ("Hello"); String s2 = "Hello"; System.out.println (S1 = = s2);//FalseSystem.out.println (s1.equals (S2));//True}}</span>

/*
* See program Write results
* String If the variable is added, first open space, in stitching.
* String If the constant is added, is added first, then in the constant pool to find, if there is a direct return, otherwise, created.
*/

<span style= "FONT-SIZE:18PX;" >public class StringDemo4 {public static void main (string[] args) {String S1 = "Hello"; String s2 = "World"; String s3 = "HelloWorld"; System.out.println (S3 = = S1 + s2);//FalseSystem.out.println (S3.equals ((S1 + s2));//trueSystem.out.println (s3 = = " Hello "+" world ");//TrueSystem.out.println (s3.equals (" Hello "+" world ");//True}}</span>

/*
* The judging function of the string class:
* Boolean equals (Object obj): Compares the contents of strings for the same, case-sensitive
* Boolean equalsignorecase (String str): Compares the contents of a string for the same, ignoring case
* Boolean contains (String str): Determines whether a large string contains a small string
* Boolean StartsWith (String str): Determines whether a string begins with a specified string
* Boolean EndsWith (String str): Determines whether the string ends with a specified string
* Boolean isEmpty (): Determines whether the string is empty.
*
Note
* The string contents are empty and the string object is empty.
* String s = "";//There is an object, but the value is empty
* String s = null;//object does not exist, so method cannot be called
*/

/*
* Get function of String class
* int Length (): Gets the length of the string.
* Char charAt (int index): Gets the character at the specified index position
* int indexOf (int ch): Returns the index of the first occurrence of the specified character in this string.
* Why is this an int type instead of a char type?
* The reason is: ' A ' and 97 can actually represent ' a ', so the int type and char type are OK, more convenient
* int indexOf (string str): Returns the index of the first occurrence of the specified string in this string.
* int indexOf (int ch,int fromIndex): Returns the index at the first occurrence of the specified character from the specified position in this string.
* int indexOf (string str,int fromIndex): Returns the index at the first occurrence of the specified string from the specified position in this string.
* String substring (int start): Intercepts the string starting at the specified position, from the default to the end.
* String substring (int start,int end): Intercepts the string from the specified position to the specified position.
*/

Requirements: Count the number of uppercase characters, lowercase alphabetic characters, number characters appearing in a string public class StringTest2 {public static void main (string[] args) {//define a string s = "Hello123world";//define three statistic variables int bigcount = 0;int Smallcount = 0;int Numbercount = 0;//iterates through the string to get each character. for (int x=0; x<s.length (); x + +) {Char ch = s.charat (x); <span style= "color: #ff0000;" >//determines whether the character belongs to that type of if (ch>= ' a ' && ch<= ' z ') {smallcount++;} else if (ch>= ' A ' && ch<= ' Z ') {bigcount++;} else if (ch>= ' 0 ' && ch<= ' 9 ') {numbercount++;} </span>}//output results. System.out.println ("Capital letter" +bigcount+ "one"); SYSTEM.OUT.PRINTLN ("Small Letter" +smallcount+ "one"); System.out.println ("number" +numbercount+ "a");}}

/*
* Conversion function of string:
* byte[] GetBytes (): Converts the string to a byte array.
* char[] ToCharArray (): Converts a string to a character array.
* Static string ValueOf (char[] CHS): Turns the character array into a string.
* Static string valueOf (int i): turns data of type int into a string.
*Note: The valueof method of the string class can turn any type of data into a string.
* String toLowerCase (): Turns the string into lowercase.
* String toUpperCase (): Turns the string into uppercase.
* String concat (String str): Concatenation of strings, convenient with + sign
*/

Requirement: The first letter of a string is capitalized and the remainder is lowercase. (only English uppercase and lowercase characters are considered) String str2 = "Listentomusic"; System.out.println (str2.substring (0, 1). toUpperCase () +str2.substring (1). toLowerCase ());

/*
* Other features of the String class:
*
* Replacement function:
* String replace (char Old,char new)
* String Replace (string old,string new)
*
* Remove string two spaces
* String Trim ()
*
* Compare two strings in a dictionary order
* int CompareTo (String str)
* int comparetoignorecase (String str)
A.compareto (b); return 0 a==b; return value >0 a>b, return value <0 a<b
*/

/* * Count the number of occurrences of a large String * Example: * In the string "woaijavawozhenaijavawozhendeaijavawozhendehenaijavaxinbuxinwoaijavagun" * Result: * Java has appeared 5 times * * Analysis: * Premise: is already aware of the large strings and small strings. * * A: Define a statistical variable, the initialization value is 0 * B: First in a large string to find the first occurrence of a small string position * A: The index is-1, the description does not exist, the return of the statistical variable * B: Index is not-1, description exists, statistical variable + + * C: The length of the previous index + string as the beginning A large string of times, returns a new string, and assigns the value of the string to a large string * D: Back to B */public class StringTest4 {public static void main (string[] args) {//define large string m axstring = "Woaijavawozhenaijavawozhendeaijavawozhendehenaijavaxinbuxinwoaijavagun";//define small string minString = "Java" ;//write function to implement int count = GetCount (maxstring, minstring); System.out.println ("Java appears in a large string:" + Count + "Times");} /* Two explicit: return value type: int parameter list: two strings */public static int GetCount (string maxstring, String minstring) {///define a statistic variable, initialize value is 0int Co UNT = 0;//First finds the first occurrence of a small string in a large string int index = Maxstring.indexof (minstring);//index is not-1, indicating existence, statistic variable ++while (Index! =-1) {count++; Take the length of the index + string as the starting position to intercept the last large string, return a new string, and re-assign the value of the string to the large string int startIndex = index + minstring.length (); maxstring = Maxstring.substring (StartIndex);//ContinueCheck index = Maxstring.indexof (minstring);} return count;}}

Java string type in the detailed