Black Horse Programmer-string Series Introduction

I. Overview

View Java source code you can find that the string class is the final type, that is, string cannot be inherited. A string is a special object that cannot be changed once it is initialized, in "abc" which case it creates a string object in memory and can be used to String s = "abc"; create a string object. You can also String s = new String("abc"); create a string object in the same way, but the difference between the two is that the former creates only one object in memory, and the latter creates two objects in memory, usually using the former to create the string object. It is also worth noting that the String s = new String(); default constructor of a string is actually creating an empty string, which is equivalent to the String s = ""; effect.
The following is a simple example of how String objects are stored in memory.

"abc"new String("abc""abc";System.out.print((s1==s2)+"/"+(s1==s3));

The output of the above program segment is:

false/true

When the program is created, it creates an s1 area in memory "abc" and points to the s1 address of the area, and when it is created, s2 two zones are created in memory, but the "abc" zone already exists and is not created again; s3 “abc” already exists in memory and is not created again. javain String fact, the object in the design mode is used to share the same string content.

Second, the common function of string to get the function

1 int length() . Gets the length of the string.
2 char charAt(int index) . Gets the character of the character index subscript position.
3, int indexOf(int ch) get the first occurrence of the string in the position of CH, no return-1 found.
4, int indexOf(int ch, int fromIndex) starting from the Fromindex position to obtain the position of CH (at this time the position or from the beginning of the calculation), did not find the return-1.
5 int indexOf(String str) . Gets the position of STR for the first time in the string, and no return-1 is found.
6, int lastIndexOf(int ch) the last occurrence of the position of CH, no return-1 found.
7, int lastIndexOf(int ch, int fromIndex) starting from the Fromindex position to obtain the last position of CH (at this point or from the beginning of the calculation), did not find the return-1.
8 int lastIndexOf(String str) . Gets the position of the last occurrence of Str in the string, no return-1 found.

Judge

1 boolean contains(CharSequence chs) . Determine if CHS (which can be a string) appears in a string.
2, boolean isEmpty() whether it is empty, and length() == 0 equivalent.
3, boolean startsWith(String str) whether to str start.
4, boolean endsWith(String str) whether to str end.
5, boolean equals(String str) whether and STR content is the same.
6, boolean equalsIgnoreCase(String str) ignore the case to determine whether the content is the same.

Transformation

1, new String(char[] chs) constructor, to replace the char array with chs a string.
2, the new String(char[] chs, int offset, int count) constructor converts the char chs characters in the array offset starting from the subscript to a count string.
3, static String copyValueOf(char[] chs) function is to char chs return the converted string according to the array.
4 static String copyValueOf(char[] chs, int offset, int count) . The function is char chs offset count converted to a string based on the characters starting from the subscript in the array.
5, static String valueOf(char[] chs) and the copyValueOf(char[] chs) same function.
6 static String valueOf(int v)/static String valueOf(long v)/... . Convert other types of variables to string types.
7, char[] toCharArray() the string is converted to a character array.
8 byte[] getBytes() . Convert the string to a byte array.

Other common functions

1, String replace(char oldChar, char newChar) oldChar replace newChar with and then return the replaced string.
2, String replace(CharSequence target, CharSequence replacement) target replace replacement with and return the replaced string.
3 String[] split(String regex) . Split this string according to the match of the given regular expression.
4 String substring(int begin) . Gets begin the string substring at the beginning of the position to the end.
5 String substring(int begin, int end) . Gets [begin, end) The string substring of the end.
6 String toUpperCase() . Convert to uppercase string.
7 String toLowerCase() . Convert to lowercase string.
8, String trim() Remove the excess space.
9, int compareTo(String str) and str comparison, if the number is less than the return negative, if it is equal to return 0, if greater than return positive. The size of the string is based on the dictionary order.

Iii. Examples of string applications

1, simulation trim() function, the function is very simple, is to remove the continuous white space can be, note that there is no space and all spaces and empty strings, the example code is as follows:

publicmyTrim(String str) {    int0, end = str.length()-1;    while‘ ‘) start ++;    while‘ ‘) end --;    return str.substring(start, end+1);}

2, the string reversal, "abcde" is about "edcba" to change, the step is to first convert the string into a character array, then flip the character array, and finally the character array to construct the string. The sample code is as follows:

publicmyReverse(String str) {    char[] chs = str.toCharArray();    for(int start=0, end=chs.length-1; start < end; start++, end--) {        char temp = chs[start];        chs[start] = chs[end];        chs[end] = temp;    }    returnnew String(chs);}

3, calculate "abkkcdkkefkkskk" kk The number of occurrences? indexOf(String, int)the ability to find the number of occurrences of a string can be accomplished by using the method. The sample code is as follows:

publicintmyCount(String str, String substr) {    int00;    while((index=str.indexOf(substr, index))!=-1) {        index += substr.length();        count ++;    }    return count;}

4. Take the longest common substring of two strings.

publicmyMaxSubstring(String s1, String s2) {    for(int i=0; i<s2.length(); i++) {        for(int j=0,k=s2.length()-i; k!=s2.length()+1; j++,k++) {            String temp = s2.substring(j, k);            if(s1.contains(temp)) {                return temp;            }        }    }    return"";}

Four StringBufferIntroduction to use

To solve String the non-changeable drawbacks, the emergence StringBuffer of classes, StringBuffer the characteristics are: variable length, you can manipulate multiple data types, such as the use of append functions to add integer, floating point, character, Boolean and other data, the end can use the toString() method return String type. StringBufferis also final a class of type.

Add Features

1, StringBuffer append(对象) here can add general types of objects, such as Integer, float, Boolean and so on. The last return StringBuffer itself, the this pointer, is called the method call chain.
2 StringBuffer insert(int offset, 对象) . You can insert a data object at the specified location, and the data after that position is postponed.

modifying features

1 StringBuffer replace(int start, int end, String str) [start, end) . Replace the segment with the str .
2 void setCharAt(int index, char ch) index . Change the character of the position to ch .
3 StringBuffer reverse() . Reverse the string.

Remove Features

1 StringBuffer delete(int start, int end) . Delete [start, end) The character contents of the segment.
2 StingBuffer deleteCharAt(int index, char ch) . Delete index the character of the position.
3, delete(0, str.length()) can be used to clear the buffer.

Other features

1, the content of the void getChars(int srcBegin, int srcEnd, char[] dst, int dstBegin) StringBuffer Middle [srcBegin, srcEnd) section is stored in the dst dstBegin location.

Wu, StringBuilder

StringBuilderand StringBuffer have compatible APIs. Appears in the JDK1.5 version. The StringBuffer biggest difference is the non- StringBuilder thread synchronization, which StringBuffer is thread synchronization.
So it is generally used in a single thread StringBuilder , because it is fast. Multi-Threading is also available StringBuilder , but locks are required.

VI. basic data type Object wrapper class

Basic data Types	class	Basic data Types	class
Byte	Byte	Float	Float
Short	Short	Double	Double
Int	Integer	Char	Character
Long	Long	Boolean	Boolean

Basic data class to String

The basic data type goes to a string in a way:

基本数据类型+"";  或者  String.valueOf();  或者  Integer.toString();等

The string to the base data type has the following example:

Integer.parseInt("123"// "123"转为123Long.parseLong("111"// "111"转为111的长整型Boolean.parseBoolean("true"// "true"转为trueInteger.parseInt("3c"16//按照16进制将"3c"转为整数，也就是60

CharacterThere is no parseCharacter method.

VII. basic data type Object wrapper class new features

The new feature in the JDK1.5 version is that objects can be directly operated between values. As follows:

4// 直接将4赋值给整型对象x，称为自动装箱，等同new Integer(4)2//直接运算，x + 2自动拆箱，然后再将和自动装箱，并赋值给xnew2//x = x + 2的具体过程。

Integeris int more than one value null . There are some of the following features:

128128127127;System.out.println(m == n);System.out.println(a == b);

The result is as follows, because when the value of integer is within the range of byte, if the value already exists in memory, the integer object is no longer created, but it points directly to the existing area.

falsetrue

Black Horse Programmer-string Series Introduction