Working with Strings in Java

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Arjit Sharma
01 Min

Creating and Initializing Strings

Strings are objects of the String class in java.lang, but Java lets you use them like primitives.

String msg = "hello world"; // Looks like a primitive, but it's an object

Common Operations in Strings

String msg = "hi" + "!!";       // Concatenation
int len = msg.length();         // Length of the string
int pos = msg.indexOf("l");     // First index of a character
String updated = msg.replace('!','*'); // Replace characters

Escape Sequences

String quote = "hello \"Arjit\""; // to put double quotes inside double quotes
String path = "c:\\Windows\\";    // Escaping backslashes
String layout = "Hello\nWorld\tHi"; // New line and tab

🔒 Note: Strings Are Immutable
Once created, a String cannot be changed. Operations like .replace() or .concat() return new strings.
👉 For repeated modifications, use StringBuilder.

String Comparison

String a = "hello";
String b = new String("hello");

// ❌ Wrong: compares references
if (a == b) { ... }

// ✅ Right: compares values
if (a.equals(b)) { ... }

String Cheatsheet

char[] vowels = {'a', 'e', 'i', 'o', 'u'};
String s = "aeiou";
String s2 = new String("welcome");

s1.equals(s2);             // Value comparison
s1.equalsIgnoreCase(s2);   // Ignore case
s1.compareTo(s2);          // Lexicographical comparison
String joined = s1 + s2;   // Concatenation
s.substring(0, 2);         // "he" from "hello"
s.length();                // Length
s.charAt(0);               // First character
s.toCharArray();           // Convert to char array
s.toLowerCase();           // Lowercase
s.toUpperCase();           // Uppercase
s.trim();                  // Remove leading/trailing whitespace
String date = String.join(":", "1", "1", "2020"); // "1:1:2020"
String[] tokens = s.split("\\s"); // Split by whitespace

StringBuilder Cheatsheet

StringBuilder sb = new StringBuilder("arjit");

sb.append(" sharma");
sb.insert(0, "Mr. ");
sb.replace(0, 2, "Mister");
sb.delete(0, 7);
sb.reverse();
sb.substring(0, 3);
sb.charAt(0);
sb.setCharAt(0, 'A');
sb.toString();
String reversed = sb.reverse().toString(); // reverse

char[] dest = new char[10];
sb.getChars(0, 4, dest, 3);  // Copy chars from sb into dest array
sb.codePointAt(0);          // Unicode of char at index
sb.codePointBefore(1);      // Unicode before index
sb.indexOf("a");
sb.lastIndexOf("a");

Character Utility Class

char ch = 'A';

Character.isDigit(ch);
Character.isLetter(ch);
Character.isLowerCase(ch);
Character.isUpperCase(ch);
Character.isWhitespace(ch);
Character.isLetterOrDigit(ch);
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