Java String replace()

The Java String class replace() method returns a string replacing all the old char or CharSequence to new char or CharSequence.

Since JDK 1.5, a new replace() method is introduced that allows us to replace a sequence of char values.

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);
}}

Test it Now

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);
}}

Test it Now

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)

Next TopicJava String replaceAll()

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