public class StringsExample {
  public static void main(String[] args) {

    String a = " Hello ";

    a = a.trim();
    System.out.println("trim: " + a);

    String b = a.concat("World");// or a+"World"
    System.out.println("concat: " + b);

    String c = b.toLowerCase();
    System.out.println("toLowerCase: " + c);

    String d = b.toUpperCase();
    System.out.println("toUpperCase: " + d);

    boolean e = d.contains("W");
    System.out.println("contains: " + e);

    // substring from idx 0 to 5
    String hello = d.substring(0,5);
    System.out.println("substring: " + e);

    int firstL = hello.indexOf('L')
    System.out.println("index of char: " + firstL);

    int lastL = hello.lastIndexOf('L')
    System.out.println("last index of char: " + lastL);

    // char at idx 0
    char firstChar = hello.charAt(0);
    // if index is out of bounds it throws an exception
    System.out.println("char at index: " + firstChar);
  }
}

 javac StringsMethods.java
 java StringsMethods

• output:

trim: Hello
concat: HelloWorld
toLowerCase: helloworld
toUpperCase: HELLOWORLD
contains: true
substring: HELLO
index of char: 2
last index of char: 3
char at index: H