HowToDoInJava

  • Python
  • Java
  • Spring Boot
  • Dark Mode
Home / Java / String / Java String concat() method example

Java String concat() method example

The Java String concat() method concatenates the method argument string to the end of string object.

1. String concat(String str) method

Internally, Java creates a new character array with combined length of string object and argument string, and copies all content from both strings into this new array. Finally, combiner character array is converted to string object.

public String concat(String str) 
{
    int otherLen = str.length();
    if (otherLen == 0) {
        return this;
    }
    int len = value.length;
    char buf[] = Arrays.copyOf(value, len + otherLen);
    str.getChars(buf, len);
    return new String(buf, true);
}

2. Java String concat example

Java program to concatenate two strings to produce combined string. We can pass an empty string as method argument. In this case, method will return the original string.

public class StringExample 
{
    public static void main(String[] args) 
    {
        System.out.println("Hello".concat(" world"));
    }
}

Program output.

Hello world

3. ‘null’ is not allowed

A 'null' argument is not allowed. It will throw NullPointerException.

public class StringExample 
{
    public static void main(String[] args) 
    {
        System.out.println("Hello".concat( null ));
    }
}

Program output.

Exception in thread "main" java.lang.NullPointerException
	at java.lang.String.concat(String.java:2014)
	at com.StringExample.main(StringExample.java:9)

Happy Learning !!

References:

Java String Doc

Was this post helpful?

Let us know if you liked the post. That’s the only way we can improve.
TwitterFacebookLinkedInRedditPocket

About Lokesh Gupta

A family guy with fun loving nature. Love computers, programming and solving everyday problems. Find me on Facebook and Twitter.

Comments are closed on this article!

Search Tutorials

String methods

  • String concat()
  • String hashCode()
  • String contains()
  • String compareTo()
  • String compareToIgnoreCase()
  • String equals()
  • String equalsIgnoreCase()
  • String charAt()
  • String indexOf()
  • String lastIndexOf()
  • String intern()
  • String split()
  • String replace()
  • String replaceFirst()
  • String replaceAll()
  • String substring()
  • String startsWith()
  • String endsWith()
  • String toUpperCase()
  • String toLowerCase()

String examples

  • Convert String to int
  • Convert int to String
  • Convert String to long
  • Convert long to String
  • Convert CSV String to List
  • Java StackTrace to String
  • Convert float to String
  • String – Alignment
  • String – Immutable
  • String – StringJoiner
  • Java – Split string
  • String – Escape HTML
  • String – Unescape HTML
  • String – Convert to title case
  • String – Find duplicate words
  • String – Left pad a string
  • String – Right pad a string
  • String – Reverse recursively
  • String – Leading whitespaces
  • String – Trailing whitespaces
  • String – Remove whitespaces
  • String – Reverse words
  • String – Find duplicate characters
  • String – Check empty string
  • String – Get first 4 characters
  • String – Get last 4 characters
  • String – (123) 456-6789 pattern
  • String – Interview Questions

Java Tutorial

  • Java Introduction
  • Java Keywords
  • Java Flow Control
  • Java OOP
  • Java Inner Class
  • Java String
  • Java Enum
  • Java Collections
  • Java ArrayList
  • Java HashMap
  • Java Array
  • Java Sort
  • Java Clone
  • Java Date Time
  • Java Concurrency
  • Java Generics
  • Java Serialization
  • Java Input Output
  • Java New I/O
  • Java Exceptions
  • Java Annotations
  • Java Reflection
  • Java Garbage collection
  • Java JDBC
  • Java Security
  • Java Regex
  • Java Servlets
  • Java XML
  • Java Puzzles
  • Java Examples
  • Java Libraries
  • Java Resources
  • Java 14
  • Java 12
  • Java 11
  • Java 10
  • Java 9
  • Java 8
  • Java 7

Meta Links

  • About Me
  • Contact Us
  • Privacy policy
  • Advertise
  • Guest and Sponsored Posts

Recommended Reading

  • 10 Life Lessons
  • Secure Hash Algorithms
  • How Web Servers work?
  • How Java I/O Works Internally?
  • Best Way to Learn Java
  • Java Best Practices Guide
  • Microservices Tutorial
  • REST API Tutorial
  • How to Start New Blog

Copyright © 2020 · HowToDoInjava.com · All Rights Reserved. | Sitemap

  • Sealed Classes and Interfaces