String
1, the string type String itself is declared final, means that we can not inherit String.
2, the target character string is immutable objects, meaning that once modified, the new object is generated
We modified the string, if you want to get new content, must be re-accepted.
3, String internal object is saved with the array of characters
After there is a char [] value array, JDK1.9 byte [] array before JDK1.9
. 4, this class String char [] values are final modification of the array, means that the array can not be changed, then it is the private modifier, can not directly operate outside it, all the methods are used to provide a String object to represent a new repair
After the change of content, so ensure the immutable String object.
5, because String objects designed to be immutable, so it has a string constant pool to save a lot of constant objects can be shared
If the modification involves a large number of strings, it is recommended to use StringBuffer or StringBuilder
1, literal constant value
String str = "hello";
2, using the constructor
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String(String original): Initializes a newly createdStringobjects to represent the same parameters as a sequence of characters; in other words, the newly created string is a copy of the argument string. -
public String(char[] value): To construct a new String by the current character array argument. -
public String(char[] value,int offset, int count): To construct a new String by part of an array of characters. -
public String(byte[] bytes): To construct a new String by using the platform's default character set to decode the current byte array parameter. -
public String(byte[] bytes,String charsetName): Construction of new String by using the specified character set currently decoded byte array parameter.
3, static methods
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static String copyValueOf (char [] data, int offset, int count): Returns the array representing the sequence of characters String
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String static valueOf (char [] Data): Returns the array representing the sequence of characters String
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static String valueOf (char [] data, int offset, int count): Returns the array representing the sequence of characters String
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String static valueOf (XX value): XX supports a variety of data types, the parameter value returns the string representation of various data types.
4、xx.toString()
S = the StringBuffer new new the StringBuffer (XX);
String = s.toString STR ();: return a String object
5, and the string stitching +
And any data type "String" is spliced, the result is a string
String str = "hello"; //1个
String str = new String("atguigu"); //2个
String s1 = "hello";//1个
String s2 = "world";//1个
String s3 = s1 + s2 + "java"; // "java" 1 th, s1 + s2 splicing a result, a final result
1、+
(1) + Constant Constant: The result is constant pool
(3) call intern after splicing method: The results in the constant pool
2, concat: the result is a mosaic of new string, even if it is two constants mosaic objects are in the heap
S1 = String "Hello";
String S2 = "World";
String S1 + S3 = "World"; // string content is HelloWorld S3, S1 is variable, "world" constants, variables, constants result in a heap +
String s4 = s1 + s2; // s4 string contents are helloworld, s1 and s2 are variables, outcome variables variables in the heap +
1 ==: Compare Address
2, equals (xx): compare string contents, strictly case-sensitive. Because String type override equals
3, equalsIgnoreCase (xx): comparison string content, case-insensitive
4, compareTo (xx): Comparison of the size of the string, character encoding in accordance with the comparison value, strictly case sensitive. String type rewrite Comparable interface of abstract methods, natural ordering
5, (xx) compareToIgnoreCase: comparing the size of the string, character code values according to the comparison case-insensitive
String str1 = "";
String str2 = new String();
String str3 = new String("");
To determine whether a string is an empty string
if("".equals(str)) //推荐
if(str!=null && str.isEmpty())
if(str!=null && str.equals(""))
if(str!=null && str.length()==0)
| The method of signature | Methods Features | |
|---|---|---|
| 1 | String() | Creating an empty string |
| 2 | String(String original) | Create a new string from the original |
| 3 | static String valueOf(xx value) | Create a string value based on content |
| 4 | String intern() | The contents of the string stored in the constant pool |
| 5 | String concat() | String concatenation |
| 6 | boolean equals(Object obj) | Determine the current string with the specified string content is already in strictly case-sensitive |
| 7 | boolean equalsIgnoreCase(String obj) | Current string is determined whether the contents of a specified string is case insensitive, |
| 8 | int compareTo(String str) | Compare the size of the current string with the specified string, strictly case-sensitive |
| 9 | int compareToIgnoreCase(String str) | Compare the current size of the string with the specified string, case-insensitive |
| 10 | boolean isEmpty() | Determining whether the current string is empty |
| 11 | int length() | Returns the string length of the current |
| 12 | String toLowerCase() | The current string lowercase |
| 13 | String toUpperCase() | The current string to uppercase |
| 14 | String trim() | White space before and after the current string is removed |
| 15 | boolean contains(xx) | Determining whether the current string comprising xx |
| 16 | int indexOf(xx) | Xx Find the first occurrence of the string in the current index |
| 17 | int lastIndexOf(xx) | Find the last occurrence of the subscript xx in the current string |
| 18 | String substring(int beginIndex) | 从当前字符串的[beginIndex, 最后]截取一个子串 |
| 19 | String substring(int beginIndex, int endIndex) | 从当前字符串的[beginIndex, endIndex)截取一个子串 |
| 20 | char charAt(index) | 返回当前字符串[index]位置字符 |
| 21 | char[] toCharArray() | 将当前字符串的内容用一个字符数组返回 |
| 22 | String(char[] value) | 用value字符数组的元素构建一个新字符串 |
| 23 | String(char[] value,int offset, int count) | 用value字符数组的[offset]开始的count个字符构建一个新字符串 |
| 24 | static String copyValueOf(char[] data) | 用data字符数组的元素构建一个新字符串 |
| 25 | static String copyValueOf(char[] data, int offset, int count) | 用data字符数组的[offset]开始的count个字符构建一个新字符串 |
| 26 | static String valueOf(char[] data) | 用data字符数组的元素构建一个新字符串 |
| 27 | static String valueOf(char[] data, int offset, int count) | 用data字符数组的[offset]开始的count个字符构建一个新字符串 |
| 28 | byte[] getBytes() | 将当前字符串按照平台默认字符编码方式编码为字节序列 |
| 29 | byte[] getBytes(字符编码方式) | 将当前字符串按照指定字符编码方式编码为字节序列 |
| 30 | String(byte[] bytes) | 将bytes字节序列按照平台默认字符编码方式解码为字符串 |
| 31 | String(byte[] bytes,String charsetName) | 将bytes字节序列按照指定字符编码方式解码为字符串 |
| 32 | boolean startsWith(xx) | 判断当前字符串是否以xx开头 |
| 33 | boolean endsWith(xx) | 判断当前字符串是否以xx结尾 |
| 34 | boolean matchs(xx) | 判断当前字符串是否满足xx正则 |
| 35 | String replace(xx,yy) | 将当前字符串中所有xx替换为yy |
| 36 | String replaceFirst(xx，value) | 将当前字符串中第一个满足xx正则的字符替换为value |
| 37 | String repalceAll(xx， value) | 将当前字符串中所有满足xx正则的字符替换为value |
| 38 | String[] split(xx) | 将当前字符串按照xx正则拆分为多个字符串 |
| 39 | void getChars(int srcBegin, int srcEnd, char[] dst, int dstBegin) | 将当前字符串的[srtBegin,srcEnd)部分字符复制到dst字符数组中，dst数组从[dstBegin]开始存储 |
String类的对象是不可变字符序列，StringBuffer和StringBuilder的对象是可变字符序列。
StringBuilder：JDK1.5之后引入的，线程不安全，单线程情况下推荐使用。
常用的API，StringBuilder、StringBuffer的API是完全一致的
StringBuilder、StringBuffer的API
| 方法签名 | 方法区功能简介 | |
|---|---|---|
| 1 | StringBuffer() | 创建一个空的可变字符序列，默认长度16 |
| 2 | StringBuffer(String str) | 用字符串str内容创建一个可变字符序列 |
| 3 | StringBuffer append(数据类型 b) | 在当前字符序列后面追加b |
| 4 | StringBufferinsert(int index, 数据类型 s) | 在当前字符序列[index]插入s |
| 5 | StringBuffer delete(int start, int end) | 删除当前字符序列[start,end)部分字符 |
| 6 | StringBuffer deleteCharAt(int index) | 删除当前字符序列[index]位置字符 |
| 7 | void setLength(int newLength) | 修改当前字符序列的长度为newLength |
| 8 | void setCharAt(int index, char ch) | 替换当前字符序列[index]位置字符为ch |
| 9 | StringBuffer reverse() | 将当前字符序列内容反转 |
| 10 | StringBuffer replace(int start, int end, String str) | 替换当前字符序列[start,end)部分字符为str |
| 11 | int indexOf(String str) | 在当前字符序列中开始查找str第一次出现的下标 |
| 12 | int indexOf(String str, int fromIndex) | 在当前字符序列[fromIndex]开始查找str第一次出现的下标 |
| 13 | int lastIndexOf(String str) | 在当前字符序列中开始查找str最后一次出现的下标 |
| 14 | int lastIndexOf(String str, int fromIndex) | 在当前字符序列[fromIndex]开始查找str最后一次出现的下标 |
| 15 | String substring(int start) | 截取当前字符序列[start,最后]部分构成一个字符串 |
| 16 | String substring(int start, int end) | 截取当前字符序列[start,end)部分构成一个字符串 |
| 17 | String toString() | 将当前可变字符序列的内容用String字符串形式表示 |
| 18 | void trimToSize() | 如果缓冲区大于保存当前字符序列所需的存储空间，则将重新调整其大小，以便更好地利用存储空间。 |
| 19 | int length() | 返回当前字符序列的长度 |
| 20 | char charAt(int index) | 返回当前字符序列[index]位置字符 |
| 21 | void getChars(int srcBegin, int srcEnd, char[] dst, int dstBegin) | 将当前字符串的[srtBegin,srcEnd)部分字符复制到dst字符数组中，dst数组从[dstBegin]开始存储 |
正则表达式
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32～126(共95个)是字符(32是空格），其中48～57为0到9十个阿拉伯数字。
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65～90为26个大写英文字母，97～122号为26个小写英文字母，其余为一些标点符号、运算符号等。
为解决一个问题：如果一份文档中含有不同国家的不同语言的字符，那么无法在一份文档中显示所有字符。Unicode字符集涵盖了目前人类使用的所有字符，并为每个字符进行统一编号，分配唯一的字符码（Code Point）
UTF-8
Unicode只是定义了一个庞大的、全球通用的字符集，并为每个字符规定了唯一确定的编号，具体存储成什么样的字节流，取决于字符编码方案。推荐的Unicode编码是UTF-16
和UTF-8。