Java教程-Java String replace()方法

Java String replace()方法

Java String类的replace()方法用于将所有旧字符或CharSequence替换为新字符或CharSequence。

自JDK 1.5以来，引入了一种新的replace()方法，允许我们替换一系列char值。

语法

Java String类中有两种replace()方法。

public String replace(char oldChar, char newChar)    
public String replace(CharSequence target, CharSequence replacement)    

自JDK 1.5以后添加了第二种replace()方法。

参数

oldChar：旧字符

newChar：新字符

target：目标字符序列

replacement：替换字符序列

返回值

替换后的字符串

异常抛出

NullPointerException：如果replacement或target为null。

内部实现

public String replace(char oldChar, char newChar) {    
       if (oldChar != newChar) {    
           int len = value.length;    
           int i = -1;    
           char[] val = value; /* 避免 getfield 操作码 */    
    
           while (++i < len) {    
               if (val[i] == oldChar) {    
                   break;    
               }    
           }    
           if (i < len) {    
               char buf[] = new char[len];    
               for (int j = 0; j < i; j++) {    
                   buf[j] = val[j];    
               }    
               while (i < len) {    
                   char c = val[i];    
                   buf[i] = (c == oldChar) ? newChar : c;    
                   i++;    
               }    
               return new String(buf, true);    
           }    
       }    
       return this;    
   }    

public String replace(CharSequence target, CharSequence replacement)  
{         
    return Pattern.compile(target.toString(), Pattern.LITERAL).matcher(  
this).replaceAll(Matcher.quoteReplacement(replacement.toString()));  
}  

Java String replace(char old, char new)方法示例

文件名：ReplaceExample1.java

public class ReplaceExample1{  
public static void main(String args[]){  
String s1="javatpoint is a very good website";  
String replaceString=s1.replace('a','e');//将所有出现的“a”替换为“e”
System.out.println(replaceString);  
}}  

输出：

jevetpoint is e very good website

Java String replace(CharSequence target, CharSequence replacement) 方法示例

文件名：ReplaceExample2.java

public class ReplaceExample2{  
public static void main(String args[]){  
String s1="my name is khan my name is java";  
String replaceString=s1.replace("is","was");//将所有出现的“is”替换为“was“
System.out.println(replaceString);  
}}  

输出：

my name was khan my name was java

Java String replace()方法示例3

文件名：ReplaceExample3.java

public class ReplaceExample3 {  
    public static void main(String[] args) {  
        String str = "oooooo-hhhh-oooooo";  
        String rs = str.replace("h","s"); // 将“h”替换为“s”
        System.out.println(rs);  
        rs = rs.replace("s","h"); // 将“s”替换为“h”
        System.out.println(rs);  
    }  
}  

输出：

oooooo-ssss-oooooo
oooooo-hhhh-oooooo

Java String replace()方法示例4

当replacement或target为null时，replace()方法会抛出NullPointerException异常。以下示例证实了这一点。

文件名：ReplaceExample4.java

public class ReplaceExample4   
{  
// main method  
public static void main(String argvs[])  
{  
  
String str = "For learning Java, JavaTpoint is a very good site.";  
int size = str.length();  
  
System.out.println(str);  
String target = null;  
  
// 用 JavaTpoint 替换 null。因此，引发了 NullPointerException。
str = str.replace(target, "JavaTpoint ");  
  
System.out.println(str);  
  
}  
}  

输出：

For learning Java, JavaTpoint is a very good site.
Exception in thread "main" java.lang.NullPointerException
    at java.base/java.lang.String.replace(String.java:2142)
    at ReplaceExample4.main(ReplaceExample4.java:12)