[!INDEX]

1. trim, lenght, isEmpty, equal { s1.mt() } + validation
2. compair to , compairToIgnoreCase (lexiographly)
3. string with +
4. concat , join, Subsequence, substring, indexOf, lastIndexOf,
5. syntax for class, boolean mt ( equals for object )

1. trim, lenght, isEmpty, equal { s1.mt() } + validation

package package2;
public class Main1 {
    public static void main(String[] args) {
        String s1 = "  bull shit  ";  
        String s2 = "  Bull shit  ";  
        String s3 = null;    
        System.out.println("S3 = "+s1.length()); // 2
        System.out.println("S3 = "+s1.isEmpty()); // false
        System.out.println("S3 = "+s1.trim()); // bull shit
        System.out.println(s1.equals(s2)); // false
        System.out.println(s1.equalsIgnoreCase(s2)); // true
        if(s1.length()==0){
            System.out.println("enter the details"); //lenght
        }
        if(s1.isEmpty()){
            System.out.println("enter the details"); //isEmpty
        }
        if(s1.trim().length()==0){
            System.out.println("enter the details"); //trim
        }
        if(s1.equals("")){
            System.out.println("enter the details");//equal
        }
    }

}

2.compair to , compairToIgnoreCase (lexiographly)

public class Main1 {
    public static void main(String[] args) {
         /* compair to A=65, a=97 */      
         String s1 = "a"; // 97
         String s2 = "A"; // 65
         System.out.println(s1.compareTo(s2)); // 32
         System.out.println(s2.compareTo(s1)); // -32
       /* compair to A=65, a=97 */        
         String s3 = "abc";
         String s4 = "Abc";
         System.out.println(s3.compareTo(s4)); // 32
       /* compair to B=66, b= 98*/        
         String s5 = "abc";
         String s6 = "aBc";
         System.out.println(s5.compareTo(s6)); // 32
       /* compair to ignore case */                
         System.out.println(s5.compareToIgnoreCase(s6)); // 0
       /* finding the lenght */
         String s7 = "b";        
         String s8 = "";        
         System.out.println(s7.compareTo(s8)); // 1, always
       /* chart link https://www.w3schools.com/charsets/ref_html_ascii.asp */
         }
}

3. string with +

package package2;
public class Main1 {
    public static void main(String[] args) {
        String s1 = "- - -";
        String s2 = "CCC";
        String s3 ="1234567890";        
        String s4 ="12345 12345";                
    /*  + mt  */    
        System.out.println(s1+s2); //- - -CCC
        System.out.println(s1+10); //- - -10
        System.out.println(s1+10+20); //- - -1020
        System.out.println(10+20+s1); //30- - -
        System.out.println(10+s1+20); //10- - -20
        System.out.println(s1+20/10); //- - -2
        System.out.println(s1+20*10); //- - -200
        System.out.println(s1+10-5); // java.lang.Error: Unresolved compilation problem
    /* concat */        

    }
}

4. concat , join, Subsequence, substring, indexOf, lastIndexOf,

package package2;
public class Main1 {
    public static void main(String[] args) {
        String s1 = "- - -";
        String s2 = "CCC";
        String s3 ="1234567890";        
        String s4 ="12345 12345"; 
        System.out.println(s1.concat(s2)); //- - -CCC
    /* join m/T, static m/T,JDK 1.8, delimiter is null -> java.lang.NullPointerException*/
        System.out.println(String.join(",",s1,s2)); // - - -,CCC
    /* subSequence , return character */
        System.out.println(s3.subSequence(2, 4)); // 34
        System.out.println(s1.subSequence(0, -1)); // outof bound
        System.out.println(s3.subSequence(0, 0)); //
    /* subSequence , return string */
        System.out.println(s4.substring(3)); // 45 12345
        System.out.println(s4.substring(2,6)); // 345
    /* indexOf() */        
        System.out.println(s4.indexOf('2')); // 1
    /* lastindexOf() */
        System.out.println(s4.lastIndexOf('2')); // 7
      }
    }

5. replace , replaceFirst, replaceAll

package package2;
public class Main1 {
    public static void main(String[] args) {
        String s1 = "- - -";
        String s2 = "CCC";
        String s3 ="1234567890";        
        String s4 ="12345 12345"; 
    /* replace , return string */
        System.out.println(s4.replace("23", "XY")); // 1XY45 1XY45
    /* replaceFirst , return string */        
        System.out.println(s4.replaceFirst("23", "--")); // 1--45 12345
        System.out.println(s4.replaceAll("23", "**")); // 1**45 1**45
    /* replaceall with regex */
        System.out.println(s4.replaceAll("3(.)", "#")); // 12#5 12#5
        System.out.println(s4.replaceAll("4(.*)", "^")); // 123^
      }
    }

6. charAt , contains, startsWith, endsWith

package package2;
public class Main1 {
    public static void main(String[] args) {
        String s1 = "- - -";
        String s2 = "CCC";
        String s3 ="1234567890";        
        String s4 ="12345 12345"; 
    /* charAt() */
        System.out.println(s4.charAt(2)); // 3
    /* contains() */
        System.out.println(s4.contains("3")); // true
    /* startsWith() */
        System.out.println(s4.startsWith("1")); // true
    /* endswith() */
        System.out.println(s4.endsWith("5")); // true        
      }
    }

7. toUpperCase , toLowerCase, toCharArray, valueOf

package package2;
public class Main1 {
    public static void main(String[] args) {
    /* toupperCase() */  
        String s5 = "momoj";
        String s6 = "KAPIL";
        String s7 = "meerut";    
        System.out.println(s5.toUpperCase());
    /* toLowerCase */    
        System.out.println(s6.toLowerCase());    
    /* valueOf */    
        int a  =10;
        String x = String.valueOf(a); // static m/T
        System.out.println(x); //10
    /* toCharArray */    
        char[]ss = s7.toCharArray(); // string to character conversion
        System.out.println(ss); // meerut
        System.out.println(ss[1]); // e            
      }
    }