String processing in Java

Introduction

String is one of class that is mostly used in Java. This tutorial will show you some common ways to process String.

Concatenate string

There are some approaches to concatenate string in Java.

1. Using “+” operator

   String a = "Hello"
   String b = " world"
   String c = a + b
   // c = "Hello world"
   

   Actually, when concatenate String using + operator, Java compiler will convert those operations into something more efficient. Above statements may be converted into:

   String c = new StringBuilder(a).append(b).toString();
   // c = "Hello world"
   

2. Using concat() method

   String a = "Hello"
   String b = " world"
   String c = a.concat(b)
   // c = "Hello world"
   

3. Using StringBuilder

   Even the Java compiler will convert string concatenation operator ( + ) into a StringBuilder chain, there are cases when we should use StringBuilder over string concatenation using (+) operator. That when we try to concatenate string in a loop.

   String[] myStrArr = {"hello", "world", "how", "are", "you", "today"}
   StringBuilder sb = new StringBuilder();
   for (String s : myStrList) {
     sb.append(s);
   }
   String c = sb.toString();
   

Convert a List<String> into String

1. Using String.join()

   String message = String.join("-", "I", "am", "a", "newbie", "Java", "developer");
   // message: I-am-a-newbie-Java-developer
   

2. Using Stream API

   String combinedCountry = countries.stream().collect(Collectors.joining("-"));
   // combinedCountry = "Belarus-Colombia-Denmark-Egypt-Germany-Hong Kong"
   

Convert a String into array of String

    String myString = "Some thing interesting";
    String[] parts = string.split(" ");
    String part1 = parts[0]; // Some
    String part2 = parts[1]; // thing
    String part3 = parts[2]; // interesting

Convert a string representaion of integer into integer

1. Use Integer.parseInt()

   String myString = "1357";
   int myInt = Integer.parseInt(myString);
   

   Note that, this will throw NumberFormatException if input is not a valid number

   int myInt = Integer.parseInt("not valid number");
   // NumberFormatException will be thrown
   

2. Use Integer.valueOf()

   String myString = "1357";
   int myInt = Integer.valueOf(myString);
   

Note

The difference betwwen Integer.valudOf() and Integer.parseInt():

• Integer.valueOf() return a new or cached instance of java.lang.Integer class
• Integer.parseInt() returns primitive int