Common Operations of the String class and common operations of the String class

Common Operations of the String class and common operations of the String class

I. Overview of the String class

1. The value of String is an object and a constant cannot be changed.

2. The equals method of String is to compare the content of two strings.

3. String s1 = "abc" String s2 = new String ("abc") s1 has an object and s2 has two objects.

Ii. Common functions of String-acquisition and judgment

1. Get

The number of characters contained in a 1.1 string, that is, the length of the string.

Int length (): Get the length.

1.2 obtain a character at a specified position

Char charAt (int index)

1.3 obtain the position of the character in the string based on the Character

Int indexOf (int ch): returns the location where ch first appears in the string.

Int indexOf (int ch, int fromIndex): obtains the position where ch appears in the string starting from the position specified by fromIndex.

Int indexOf (String str, int fromIndex): obtains the position where ch appears in the String starting from the position specified by fromIndex. If no position is found,-1 is returned.

Int lastIndexOf (String str): reverse index where a character appears

1 public static void method_get () {2 String str = "abcdeakpf"; 3 // print the String length 4 sop (str. length (); // The result is 5 5 // obtain characters 6 sop (str. charAt (4); // The result is a 7 // obtain the index 8 sop (str. indexOf ('A', 3); // The result is 5 9 // reverse index the position where a character appears 10 sop (str. lastIndexOf ("a"); // result: 511}View Code

2. Judgment

2.1 whether the string contains a substring

Boolean contains (str)

Special: indexOf (str): You can index the position where str appears for the first time. If-1 is returned, this str does not exist in the string, therefore, it can also be used to determine whether a specified character substring is contained and obtain the position where the substring appears;

Whether there is content in 2.2 characters

Boolean isEmpty (): determines whether the length is 0.

2.3 whether the string starts with the specified content

Boolean startsWith (str );

2.4 The string ends with the specified content

Boolean endsWith (str );

2.5 check whether the string content is the same. The equals method in the Object class is rewritten.

Boolean equals (str );

2.6 check whether the content is the same. Ignore case sensitivity.

Boolean inclusignorecase ();

1 public static void method_is () {2 String str = "ArrayDemo. java "; 3 // determine whether the file name starts with Array 4 sop (str. startsWith ("Array"); // returns true5 // determines whether the file name is. java file 6 sop (str. endsWith (". java "); // The result is true7 // determine whether the file name contains the Demo Word 8 sop (str. contains ("Demo"); // The result is true9}View Code

3. String common functions-Conversion

3.1 convert the character array into a string.

Constructor: String (char [])

String (char [], offset, count): convert part of the character array into a String

Static Method:

Static String copyValueOf (char [])

Static String copyValueOf (char [], offset, count)

Static String valueOf (cahr [])

3.2 convert a string into a character array

Char [] toCharArray ();

3.3 convert byte arrays into strings

String (byte [])

String (byte [], offset, count): convert part of the byte array into a String

3.4 convert a string to a byte array

Byte [] getBytes ();

3.5 convert the basic data type to a string

Static String valueOf (int)

Static String valueOf (double)

3.6 Special: encoding tables can be specified during conversion of strings and byte arrays.

1 public static void method_trans () {2 char [] arr = {'A', 'B', 'C', 'D', 'E', 'F '}; 3 String s = new String (arr, 1, 3); 4 sop ("s =" + s); // The result is bcd 5 6 String s1 = "zxcvbnm "; 7 char [] chs = s1.toCharArray (); 8 for (int I = 0; I <chs. length; I ++) {9 sop ("ch =" + chs [I]); 10} 11}View Code

4. Replace

String replace (oldchar, newchar)

If the character to be replaced does not exist, the original string is returned.

1 public static void method_replace () {2 String s = "Hello java"; 3 String s1 = s. replace ('A', 'n'); 4 String s2 = s. replace ("java", "world"); 5 sop ("s =" + s); // The result is Hello java6 sop ("s1 =" + s1 ); // The result is Hello jnvn7 sop ("s2 =" + s2); // The result is Hello world8}View Code

5. Cutting

String [] split (regex );

1 public static void method_split () {2 String s = "zhangsan, lisi, wangwu"; 3 String [] attr = s. split (","); 4 for (int I = 0; I <attr. length; I ++) {5 sop (attr [I]); // The result is zhangsan lisi wangwu6} 7}View Code

6. substring to obtain part of the string

String substring (begin): starts from the specified position and ends. If the badge does not exist, an exception occurs when the badge is out of bounds.

String substring (begin, end): Starting from the start position to the end position, protecting the start position from not including the end position

1 public static void method_sub () {2 String s = "abcdef"; 3 sop (s. substring (2); // The result is cdef4 sop (s. substring (2, 4); // The result is cd5}View Code

7. Convert, remove spaces, and compare

7.1 convert the string to uppercase or lowercase letters

String toUpperCase ();

String toLowerCase ();

7.2 remove multiple spaces at both ends of the string

String trim ();

7.3 compare the natural order of two strings

Int compareTo (String)

1 public static void method_7 () {2 String s = "Hello Java"; 3 sop (s. toUpperCase (); 4 sop (s. toLowerCase (); 5 sop (s. trim (); 6 String s1 = "acc"; 7 String s2 = "aaa"; 8 sop (s1.compareTo (s2 )); // The result is 2 (the result of two Unicode values subtraction), indicating that s1 is greater than s29}View Code