table of Contents
Creating strings
- Quoted string constant
- String a; a = "student";
- Use the same string constants assigned to different variables, their addresses are the same (a == b), the program will look for it exists or not constant in the stack, there is a direct address assigned to a new variable instead of re-heap create objects
- Using the constructor
- String a = new String("student")
- String b = new String(a)
- Examples of the use of an array of characters
- String a = new String(char a[])
- String a = new String(char a[], int offset, int length)
- Examples of using the byte array
- String a = new String(byte a[])
Connection String
- Connecting the plurality of strings
- +
- + Time = variable name is very long, high readability
- Other types of connection
- + Operator has only one operand is a string, the compiler will convert the other operand to a string (automatically call toString () method)
Gets a string of information
- Get string length
- str.length()
- str.lastIndexOf ( ""); an empty string in a string index is equal to the length of the string
- String search
- str.indexOf (String s); s returns the index of the first occurrence of the specified string, not retrieved -1
- str.indexOf(String s, int fromIndex);
- str.lastIndexOf (String s); s return to the last location of the search string appears, not retrieved -1
- str.lastIndexOf(String s, int fromIndex);
- Gets the index position of the character
- str.charAt(int index)
String Manipulation
- Get a substring
- str.substring (int beginIndex); return carriers from index position to the end of the string
- str.substring (int beginIndex, int endIndex); return from the start to the end of the index sub-string of length endIndex - beginIndex, the last character index is not included within the meaning of
- Remove the spaces before and after the string
- str.trim();
- String replacement
- str.replace (char oldChar, char newChar); replacement character or string, no return to the original string
- str.replaceAll ( "\\ s", ""); remove all spaces, the former is a regular expression parameter, the parameter is Replaced
- Analyzing beginning and end of the string
- str.startsWith (String prefix); return value boolean type
- str.endsWith(String suffix);
- Analyzing the strings are equal
- str.equals (String otherstr);, returns a boolean value
- str.equalsIgnoreCase (String otherstr); ignore case
- Compare strings lexicographically
- str.compareTo (String otherstr); compares successive string of characters, str if after otherstr, returns a negative integer before, after returning a positive integer, the return value before or after the first few positions. Equal return 0
- str.compareToIgnoreCase(String otherstr);
- Letter case conversion
- str.toLowerCase();
- str.toUpperCase (); non-numeric character is not affected
- String split
- str.split (String sign); sign is a separator, "|" is the definition of a plurality of separators, a regular expression may be
- str.split (String sign, int limit); limit defines the number of divisions, the number is less than 0, dividing the whole greater than the maximum division number
- split will match the regular expression. means match any character, you need to use \ to escape, and \ itself needs to be escaped so \\.
Format string
String class static method formate () is used to create formatted strings.
- Date and time format string
- Need to import import java.util.Date
- Date date = new Date (); String s = String.formate (String form, date); s is the formatted string
- Conventional type format
Using regular expressions
- Regular expression metacharacters, this meta-character represents a specific set of characters
- Square brackets [] enclosed element represents a character, the element can represent any character a character [abc] 4 a4 representative of the character element, b4, c4
- [^ Abc] represents the character except abc, ^ represents the opposite
- [Az] az represents any letter, - indicates a range
- [Ae [gz]] [] was added [] represents arithmetic and
- [Ao && [def]] && represents a cross-operation
- [Ad && [^ bc]] && ^ represents the difference calculation binding
- | Represents or, && represents a cross, [] represents any one of which, indicated to the contrary ^
- Limited number modifier appears limited metacharacters
- str.matchs (String regex); return boolean
String generator
String created using the string length is fixed which, when used for connecting a plurality of strings +, will produce a new String instance, create a new string object in memory, if duplicate modification of the string, will greatly increase system overhead. JDK5 new variable sequence of characters (String-Builder) class, which greatly improves the efficiency of the frequent increase in the string.
- StringBuffer and StringBuider comparison:
- To provide compatible API, but does not guarantee StringBuider thread synchronization, the disadvantage is only in a single thread, the advantage is not locked to the thread
- StringBuffer, StringBuider, String interchangeable
- String to convert or StringBuider use StringBuffer constructor new StringBuider (String) or new StringBuider (String)
- StringBuffer, StringBuider converted into String using toString () method
- StringBuffer and StringBuider conversion method to use toString () method to a String reuse constructor
- StringBuilder builder = new StringBuider();
- StringBuilder builder = new StringBuider("123");
- StringBuilder builder = new StringBuider (32); an initial capacity of 32 characters
- append (content); add content, StringBuider return object address
- insert (int offset, arg); Inserts returns StringBuilder object
- delete (int start, in end); deleted substring and returns the object StringBuider
- setCharAt (int index, char ch); None Return Value
- Reverse (); anti-order output;
- toString (); return a String object
- String and similar methods
- int lengt = builder.length (); return string length
- char chr = builder.charAt (int index); retrieve a specified index
- int index = builder.indexOf (String str); Get index of the specified string
- String substr = builder.substring (int beginIndex, int endIndex); get a substring
- StringBuider tmp = builder.replace (int beginIndex, int endIndex, String str); replace the specified sequence of characters (with different String)
- Other class methods of the API query java.lang.StringBuilder
- StringBuffer buffer = new StringBuffer(); 同StringBuider
package ex5_String;
public class ex5_28_Jerque {
public static void main(String[] args) {
String str = "";
long starTime = System.currentTimeMillis();
for (int i = 0; i < 10000; i++) {
str += i;
}
long endTime = System.currentTimeMillis();
System.out.println("time: " + (endTime - starTime));
StringBuilder builder = new StringBuilder("");
starTime = System.currentTimeMillis();
for (int i = 0; i < 10000; i++) {
builder.append(i);
}
endTime = System.currentTimeMillis();
System.out.println("time: " + (endTime - starTime));
}
}
Exercise
- Write the phone number of regular expressions
- Use additional character string builder
package ex5_String;
public class ex5_practice_3 {
public static void main(String[] args) {
String text = "12345678912";
String regex = "1\\d{10}";
System.out.println(text + " is " + text.matches(regex) + " phone number");
StringBuilder builder = new StringBuilder("");
for (int i = 1; i<=10; i++) {
builder.append(i);
}
System.out.println(builder.toString());
}
}
