Lab Java String methods

Objective

In this lab, you will explore and demonstrate the built-in methods in the String class. These methods help you manipulate the String data type. By the end of this lab learners will be able to describe the Strings methods and use Java Strings Methods.

Instructions

length() method

The length() method returns the length of the string, or it returns the count of the total number of characters present in the string.

Example:

Public class lenthDemo {
    public static void main(String[] args) {
        String str1 = "Java";
        String str2 = "";

        System.out.println(str1.length());  // 4
        System.out.println(str2.length());  // 0
        System.out.println("Java".length());  // 4
        System.out.println("Java\\\\n".length()); // 5
        System.out.println("Learn Java".length()); // 10
    }
}

Output:

4
0
4
5
10

isEmpty() method:

This method checks whether the String contains anything or not. If the Java String is empty, it returns true or false.

Example:

public class IsEmptyExample{
public static void main(String args[]){
String s1="";
String s2="hello";
System.out.println(s1.isEmpty());      // true
System.out.println(s2.isEmpty());      // false
}}

Output:

True
False

trim() method:

The Java string trim() method removes the leading and trailing spaces. It checks the Unicode value of the space character (‘\u0020’) before and after the string. If it exists, then remove the spaces and return the omitted string.

Example:

public class StringTrimExample{
public static void main(String args[]){
String s1="  hello   ";
System.out.println(s1+"how are you");        // without trim()
System.out.println(s1.trim()+"how are you"); // with trim()
 }
}

toLowerCase() method:

The toLowerCase() method converts all the characters of the String to lowercase.

Example:

public class StringLowerExample{
 public static void main(String args[]){
    String s1="HELLO HOW Are You?";
    String s1lower=s1.toLowerCase();
    System.out.println(s1lower);}
}

Output:

hello how are you.

toUpperCase() method:

The toUpperCase() method converts all of the String characters to uppercase.

Example:

public class StringUpperExample{
  public static void main(String args[]){
    String s1="hello how are you";
    String s1upper=s1.toUpperCase();
    System.out.println(s1upper);
}}

Output:

HELLO HOW ARE YOU.

concat() method:

The Java String class provides the concat() method. This method combines a specific string at the end of another string, and ultimately returns a combined string.

Example:

public class concatDemo {
   public static void main(String[] args) {
      //------By using concat method----
       String str1 = "Learn ";
       String str2 = "Java";
       // concatenate str1 and str2
       System.out.println(str1.concat(str2)); // "Learn Java"

       // concatenate str2 and str11
       System.out.println(str2.concat(str1)); // "JavaLearn "
     //--- By using + operator---
       String s3 =  "hello";
       String s4 = "Learners";
     //  String s5 = s3.concat(s4); or
          String s5 = s3 + s4;
     //both of the above statement will give you the same result

      // Three strings are concatenated
       String message = "Welcome " + "to " + "Java";

     // String Chapter is concatenated with number 2
       String s = "Chapter" + 2; // s becomes Chapter2

   // String Supplement is concatenated with character B
       String s1 = "Supplement" + 'B'; // s1 becomes SupplementB
   }
}

split() method:

The split() method divides the string at the specified regex and returns an array of substrings.

Example:

// importing Arrays to convert array to string
// used for printing arrays
import java.util.Arrays;

public class Main {
  public static void main(String[] args) {
    String vowels = "a::b::c::d:e";

    // splitting the string at "::"
    // storing the result in an array of strings
    String[] result = vowels.split("::");

    // converting array to string and printing it
    System.out.println("result = " + Arrays.toString(result));
  }
}

Output:

result = [a, b, c, d:e]

charAt() method:

The charAt() method gets the character at the specified index.

Example:

public class concatdemo {
   public static void main(String[] args) {
   String message = "Welcome to Java";
   System.out.println("The first character in the message is " + message.charAt(0));
 }
}

compareTo() method:

The compareTo() method compares the given string with the current string.

Example:

public class CompareToExample{
public static void main(String args[]){
String s1="hello";
String s2="hello";
String s3="hemlo";
String s4="flag";
System.out.println(s1.compareTo(s2)); // 0 because both are equal
System.out.println(s1.compareTo(s3)); //-1 because "l" is only one time lower than "m"
System.out.println(s1.compareTo(s4)); // 2 because "h" is 2 times greater than "f"
}}

substring() method:

The substring() method extracts a substring from the string and returns it.

Example:

public class substringDemo{
  public static void main(String[] args) {
    String str1 = "java is fun";

    // extract substring from index 0 to 3
    System.out.println(str1.substring(0, 4));

  }
}

indexOf() method:

The indexOf() method returns the index of the first occurrence of the specified character/substring within the string.

Example:

public class findString {
   public static void main(String[] args) {
       String str1 = "Java is fun";
       int result;

       // getting index of character 's'
       result = str1.indexOf('s');

       System.out.println(result); // 6

       // getting index of character 'J'
       result = str1.lastIndexOf('J');
       System.out.println(result); // 0

       // the last occurrence of 'a' is returned
       result = str1.lastIndexOf('a');
       System.out.println(result); // 3

       // character not in the string
       result = str1.lastIndexOf('j');
       System.out.println(result); // -1

       // getting the last occurrence of "ava"
       result = str1.lastIndexOf("ava");
       System.out.println(result); // 1

       // substring not in the string
       result = str1.lastIndexOf("java");
       System.out.println(result); // -1
   }
}

contains() method:

The contains() method checks whether the specified string (sequence of characters) is present in the string or not.

Example:

Public class containexmaple {
  public static void main(String[] args) {
    String str1 = "Learn Java";
    Boolean result;

    // check if str1 contains "Java"
    result = str1.contains("Java");
    System.out.println(result);  // true

    // check if str1 contains "Python"
    result = str1.contains("Python");
    System.out.println(result);  // false

    // check if str1 contains ""
    result = str1.contains("");

    System.out.println(result);  // true
  }
}

replace() method:

The replace() method replaces each matching occurrence of the old character/text in the string with the new character/text.

Example:

public class replaceDemoMain {
  public static void main(String[] args) {
    String str1 = "abc cba";

    // all occurrences of 'a' is replaced with 'z'
    System.out.println(str1.replace('a', 'z'));

    // all occurences of 'L' is replaced with 'J'
    System.out.println("Lava".replace('L', 'J'));
    // character not in the string
    System.out.println("Hello".replace('4', 'J'));
// all occurrences of "C++" is replaced with "Java"
    System.out.println(str1.replace("C++", "Java"));

    // all occurences of "aa" is replaced with "zz"
    System.out.println("aa bb aa zz".replace("aa", "zz"));

    // substring not in the string
    System.out.println("Java".replace("C++", "C"));
  }
}

Java String compares

There are three ways to compare String in Java:

By Using equals() Method

The String class's equals() method compares the original content of the string.

Example:

public class Teststringcomparison {
   public static void main(String args[]){
       String s1="PerScholas";
       String s2="PerScholas";
       String s3=new String("PerScholas");
       String s4="Teksystem";
       System.out.println(s1.equals(s2));//true
       System.out.println(s1.equals(s3));//true
       System.out.println(s1.equals(s4));//false
   }
}

By Using == Operator

The == operator compares references, not values.

Example:

public class Teststringcomparison2 {
   public static void main(String args[]){
       String s1="Perscholas";
       String s2="Perscholas";
       String s3=new String("Perscholas");
       System.out.println(s1==s2);//true (because both refer to same instance)
       System.out.println(s1==s3);//false(because s3 refers to instance created in nonpool)
   }

}

By compareTo() Method

The compareTo() method compares values lexicographically.

Example:

public class Teststringcomparison3 {
   public static void main(String args[]){
       String s1="Perscholas";
       String s2="Perscholas";
       String s3="Perscholas";
       System.out.println(s1.compareTo(s2));//0
       System.out.println(s1.compareTo(s3));//1(because s1>s3)
       System.out.println(s3.compareTo(s1));//-1(because s3 < s1 )
   }
}