Internship
Student login

Strings

Useful methods, comparing with equals, and StringBuilder.

A String cannot be changed once created: methods return a new one.

Java
public class Main {
  public static void main(String[] args) {
    String s = "Internship";
    System.out.println(s.length());
    System.out.println(s.charAt(0));
    System.out.println(s.substring(0, 5));
    System.out.println(s.toUpperCase());
    System.out.println(s.contains("ship"));
  }
}
Output
10
I
Inter
INTERNSHIP
true

Compare with equals, not ==

== checks whether two variables point at the same object. equals() checks the text. Interviewers often ask about this.

Java
public class Main {
  public static void main(String[] args) {
    String a = "java";
    String b = new String("java");
    System.out.println(a == b);
    System.out.println(a.equals(b));
  }
}
Output
false
true

StringBuilder

Building a long string in a loop with + creates a new object each time. StringBuilder changes one buffer instead.

Java
public class Main {
  public static void main(String[] args) {
    StringBuilder sb = new StringBuilder();
    for (int i = 1; i <= 3; i++) {
      sb.append(i).append(",");
    }
    System.out.println(sb.reverse());
  }
}
Output
,3,2,1
← Variables and data typesConditions and loops →