Java字符串replaceAll()替换所有出现的特定字符，字符串或者字符串中的正则表达式。
该方法返回一个新字符串作为其输出。
该方法需要两个参数。

字符串replaceAll()语法

public String replaceAll(String regex, String replacement)

一个正则表达式，代表替换时要查找的模式以及替换它的替换字符串。

字符串replaceAll()方法可能有多种替换类型。

替换单个字符

要替换单个字符，请指定要替换的字符作为正则表达式。

public class Main {

  public static void main(String[] args) {
      String s = "Welcome to theitroad";
      System.out.println("Original String : "+s);
      System.out.println();
      String rep = s.replaceAll("o","@");
      System.out.println("New String: "+rep);
  }
}

Original String: Welcome to theitroad

New String: Welc@me t@ J@urnalDev

替换字符序列

要替换字符序列，请在replaceAll()函数中将该序列称为正则表达式。

public class Main {

  public static void main(String[] args) {
      String s = "Welcome to theitroad";
      System.out.println("Original String : "+s);
      System.out.println();
      String rep = s.replaceAll("to","this is");
      System.out.println("New String: "+rep);
  }
}

输出

Original String : Welcome to theitroad

New String: Welcome this is theitroad

删除/替换空间

replaceAll()方法可以删除或者替换文本字符串中的空格。

public class Main {

  public static void main(String[] args) {
      String s = "Welcome to theitroad";
      System.out.println("Original String : "+s);
      System.out.println();
      String rep = s.replaceAll(" ","");
      System.out.println("New String: "+rep);
  }
}

删除空间

Original String : Welcome to theitroad

New String: Welcometotheitroad

同样，要替换空白：

public class Main {

  public static void main(String[] args) {
      String s = "Welcome to theitroad";
      System.out.println("Original String : "+s);
      System.out.println();
      String rep = s.replaceAll(" ","_");
      System.out.println("New String: "+rep);
  }
}

Original String : Welcome to theitroad

New String: Welcome_to_theitroad

隐藏文本中的数字

replaceAll()可以隐藏出现在字符串中的数字。
可用" *"代替数字。

public class Main {

  public static void main(String[] args) {
      String s = "Hello! this is the number : 1234 ";
      System.out.println("Original String : "+s);
      System.out.println();
      String rep = s.replaceAll("[0-9]","*");
      System.out.println("New String: "+rep);
  }
}

Original String : Hello! this is the number : 1234 

New String: Hello! this is the number :  

创建自定义消息

replaceAll()可以替换通用字符串中的字符串以生成自定义消息。
让我们从地图中获取值并生成自定义消息。

import java.util.HashMap;
import java.util.Map;

public class Main {

  public static void main(String[] args) {
      String s = "dear #Employee#, your Current Salary is #Salary#.";
      Map<String, String> vals = new HashMap<String, String>();
      vals.put("#Employee#", "John");
      vals.put("#Salary#", "12000");
      for (String key : vals.keySet()) {
          s = s.replaceAll(key, vals.get(key));
      }
      System.out.println(s);
  }
}

dear John, your Current Salary is 12000.

首先替换

与replceAll()不同，replaceFirst()仅替换模式的第一个实例。

public class Main {

  public static void main(String[] args) {
      String s = "Welcome to theitroad";
      System.out.println("Original String : "+s);
      System.out.println();
      String rep = s.replaceFirst("o","@");
      System.out.println("New String: "+rep);
  }
}

Original String: Welcome to theitroad

New String: Welc@me to theitroad