Java String replace() Example | String replace() Function In Java

Java String replace() method returns the string replacing all the old char or CharSequence to a new char or CharSequence. At times, it is required to replace some characters in a String with a new character. It might also be required to change an entire sequence of characters with a new sequence of characters, i.e., replacing an old CharSequence with a new CharSequence. The java.lang.String.replace() method is a built-in method of the String class designed just for this purpose.

Java String replace

Java string replace() method returns the new string resulting from replacing all occurrences of old characters in the string with new characters.

Signature

There are two types of replace() methods in Java String class.

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

The second replace() method is added since JDK 1.5.

Parameters

• oldChar : old character
• newChar : new character
• target : target sequence of characters
• replacement : replacement sequence of characters

Returns

• replaced string

Exception Throws

NullPointerException: if the replacement or target is equal to null.

Internal implementation

public String replace(char oldChar, char newChar) {    
       if (oldChar != newChar) {    
           int len = value.length;    
           int i = -1;    
           char[] val = value; /* avoid getfield opcode */    
    
           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) method example

FileName: 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');//replaces all occurrences of 'a' to 'e'  
System.out.println(replaceString);  
}}  

Output:

jevetpoint is e very good website

Java String replace(CharSequence target, CharSequence replacement) method example

FileName: 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");//replaces all occurrences of "is" to "was"  
System.out.println(replaceString);  
}}  

Output:

my name was khan my name was java

Java String replace() Method Example 3

FileName: ReplaceExample3.java

public class ReplaceExample3 {  
    public static void main(String[] args) {  
        String str = "oooooo-hhhh-oooooo";  
        String rs = str.replace("h","s"); // Replace 'h' with 's'  
        System.out.println(rs);  
        rs = rs.replace("s","h"); // Replace 's' with 'h'  
        System.out.println(rs);  
    }  
}  

Output:

oooooo-ssss-oooooo
oooooo-hhhh-oooooo

Java String replace() Method Example 4

The replace() method throws the NullPointerException when the replacement or target is null. The following example confirms the same.

FileName: 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;  
  
// replacing null with JavaTpoint. Hence, the NullPointerException is raised.  
str = str.replace(target, "JavaTpoint ");  
  
System.out.println(str);  
  
}  
}  

Output:

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)

#java #replace()