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📜  Java-字符串类

📅  最后修改于: 2020-12-21 01:37:22             🧑  作者: Mango

在Java编程中广泛使用的字符串是字符序列。在Java编程语言中，字符串被视为对象。

Java平台提供String类来创建和操作字符串。

创建字符串

创建字符串的最直接方法是编写-

String greeting = "Hello world!";

每当在代码中遇到字符串字面量时，编译器都会创建一个String对象，其值在这种情况下为“ Hello world！”。

与其他任何对象一样，您可以使用new关键字和构造函数来创建String对象。 String类具有11个构造函数，可让您使用不同的来源(例如，字符数组)提供字符串的初始值。

例

现场演示

public class StringDemo {

   public static void main(String args[]) {
      char[] helloArray = { 'h', 'e', 'l', 'l', 'o', '.' };
      String helloString = new String(helloArray);  
      System.out.println( helloString );
   }
}

这将产生以下结果-

输出

hello.

注– String类是不可变的，因此一旦创建它，就不能更改String对象。如果有必要做出了很多修改的字符的字符串，那么你应该使用字符串缓冲区和字符串构建类。

弦长

用于获取有关对象的信息的方法称为访问器方法。可以与字符串使用的一种访问器方法是length()方法，该方法返回字符串对象中包含的字符数。

以下程序是String类的length()方法的示例。

例

现场演示

public class StringDemo {

   public static void main(String args[]) {
      String palindrome = "Dot saw I was Tod";
      int len = palindrome.length();
      System.out.println( "String Length is : " + len );
   }
}

这将产生以下结果-

输出

String Length is : 17

连接字符串

String类包括用于连接两个字符串的方法-

string1.concat(string2);

这将返回一个新字符串，该字符串为string1，最后添加了string2。您还可以将concat()方法与字符串字面量，如-

"My name is ".concat("Zara");

字符串通常与＆plus;连接在一起。运算符，如-

"Hello," + " world" + "!"

这导致-

"Hello, world!"

让我们看下面的例子-

例

现场演示

public class StringDemo {

   public static void main(String args[]) {
      String string1 = "saw I was ";
      System.out.println("Dot " + string1 + "Tod");
   }
}

这将产生以下结果-

输出

Dot saw I was Tod

创建格式字符串

您可以使用printf()和format()方法来打印带有格式化数字的输出。 String类具有等效的类方法format()，该方法返回String对象而不是PrintStream对象。

通过使用String的静态format()方法，您可以创建可重复使用的格式化字符串，而不是一次性打印语句。例如，代替-

例

System.out.printf("The value of the float variable is " +
                  "%f, while the value of the integer " +
                  "variable is %d, and the string " +
                  "is %s", floatVar, intVar, stringVar);

你可以写-

String fs;
fs = String.format("The value of the float variable is " +
                   "%f, while the value of the integer " +
                   "variable is %d, and the string " +
                   "is %s", floatVar, intVar, stringVar);
System.out.println(fs);

字符串方法

这是String类支持的方法列表-

Sr.No. Method & Description
1 char charAt(int index)

Returns the character at the specified index.
2 int compareTo(Object o)

Compares this String to another Object.
3 int compareTo(String anotherString)

Compares two strings lexicographically.
4 int compareToIgnoreCase(String str)

Compares two strings lexicographically, ignoring case differences.
5 String concat(String str)

Concatenates the specified string to the end of this string.
6 boolean contentEquals(StringBuffer sb)

Returns true if and only if this String represents the same sequence of characters as the specified StringBuffer.
7 static String copyValueOf(char[] data)

Returns a String that represents the character sequence in the array specified.
8 static String copyValueOf(char[] data, int offset, int count)

Returns a String that represents the character sequence in the array specified.
9 boolean endsWith(String suffix)

Tests if this string ends with the specified suffix.
10 boolean equals(Object anObject)

Compares this string to the specified object.
11 boolean equalsIgnoreCase(String anotherString)

Compares this String to another String, ignoring case considerations.
12 byte[] getBytes()

Encodes this String into a sequence of bytes using the platform’s default charset, storing the result into a new byte array.
13 byte[] getBytes(String charsetName)

Encodes this String into a sequence of bytes using the named charset, storing the result into a new byte array.
14 void getChars(int srcBegin, int srcEnd, char[] dst, int dstBegin)

Copies characters from this string into the destination character array.
15 int hashCode()

Returns a hash code for this string.
16 int indexOf(int ch)

Returns the index within this string of the first occurrence of the specified character.
17 int indexOf(int ch, int fromIndex)

Returns the index within this string of the first occurrence of the specified character, starting the search at the specified index.
18 int indexOf(String str)

Returns the index within this string of the first occurrence of the specified substring.
19 int indexOf(String str, int fromIndex)

Returns the index within this string of the first occurrence of the specified substring, starting at the specified index.
20 String intern()

Returns a canonical representation for the string object.
21 int lastIndexOf(int ch)

Returns the index within this string of the last occurrence of the specified character.
22 int lastIndexOf(int ch, int fromIndex)

Returns the index within this string of the last occurrence of the specified character, searching backward starting at the specified index.
23 int lastIndexOf(String str)

Returns the index within this string of the rightmost occurrence of the specified substring.
24 int lastIndexOf(String str, int fromIndex)

Returns the index within this string of the last occurrence of the specified substring, searching backward starting at the specified index.
25 int length()

Returns the length of this string.
26 boolean matches(String regex)

Tells whether or not this string matches the given regular expression.
27 boolean regionMatches(boolean ignoreCase, int toffset, String other, int ooffset, int len)

Tests if two string regions are equal.
28 boolean regionMatches(int toffset, String other, int ooffset, int len)

Tests if two string regions are equal.
29 String replace(char oldChar, char newChar)

Returns a new string resulting from replacing all occurrences of oldChar in this string with newChar.
30 String replaceAll(String regex, String replacement

Replaces each substring of this string that matches the given regular expression with the given replacement.
31 String replaceFirst(String regex, String replacement)

Replaces the first substring of this string that matches the given regular expression with the given replacement.
32 String[] split(String regex)

Splits this string around matches of the given regular expression.
33 String[] split(String regex, int limit)

Splits this string around matches of the given regular expression.
34 boolean startsWith(String prefix)

Tests if this string starts with the specified prefix.
35 boolean startsWith(String prefix, int toffset)

Tests if this string starts with the specified prefix beginning a specified index.
36 CharSequence subSequence(int beginIndex, int endIndex)

Returns a new character sequence that is a subsequence of this sequence.
37 String substring(int beginIndex)

Returns a new string that is a substring of this string.
38 String substring(int beginIndex, int endIndex)

Returns a new string that is a substring of this string.
39 char[] toCharArray()

Converts this string to a new character array.
40 String toLowerCase()

Converts all of the characters in this String to lower case using the rules of the default locale.
41 String toLowerCase(Locale locale)

Converts all of the characters in this String to lower case using the rules of the given Locale.
42 String toString()

This object (which is already a string!) is itself returned.
43 String toUpperCase()

Converts all of the characters in this String to upper case using the rules of the default locale.
44 String toUpperCase(Locale locale)

Converts all of the characters in this String to upper case using the rules of the given Locale.
45 String trim()

Returns a copy of the string, with leading and trailing whitespace omitted.
46 static String valueOf(primitive data type x)

Returns the string representation of the passed data type argument.