Strings & String Methods

Syntax

String variableName = "text";

Examples

String firstName = "Fola";
String lastName = "A";

String fullName = firstName + " " + lastName;
System.out.println(fullName);  // Fola A

String greeting = String.format("Hello, %s!", firstName);
System.out.println(greeting);

String text = "  Hello World  ";

System.out.println(text.length());       // 15 (includes whitespace)
System.out.println(text.trim());          // "Hello World"
System.out.println(text.toUpperCase());   // "  HELLO WORLD  "
System.out.println(text.toLowerCase());   // "  hello world  "

String sentence = "The quick brown fox";

System.out.println(sentence.contains("quick"));    // true
System.out.println(sentence.indexOf("brown"));      // 10
System.out.println(sentence.substring(4, 9));        // "quick"
System.out.println(sentence.replace("fox", "dog"));  // The quick brown dog

String csv = "Fola,Zain,Jamal";
String[] names = csv.split(",");

for (String name : names) {
    System.out.println(name);
}

String joined = String.join(" & ", names);
System.out.println(joined);  // Fola & Zain & Jamal

Best practices

• Remember String is immutable - every method like .trim() or .toUpperCase() returns a new String rather than modifying the original
• Use a StringBuilder instead of repeated + concatenation when building a string inside a loop, for much better performance
• Use .equals() (or .equalsIgnoreCase()) for content comparison, never == for comparing String values
• Use String.format() or printf-style formatting for building strings with embedded numbers or aligned output, rather than manual concatenation

At a glance

Purpose

General-purpose application development

File extension

.java

Runs in

Java Virtual Machine

Usually used with

JDK and Java libraries

Specifications & further reading

• Java Language Specification

Related Java documentation