String(uppercase to lowercase,replace)

package stringuppertolower;

public class StringUpperToLower {

    public static void main(String[] args) {
        
        String name="Abdul Mukit";
        System.out.println("Before change:"+name);
        
        String change=name.toLowerCase();
        System.out.println("After change:"+change);
        
        char c=name.charAt(1);
        System.out.println("CharAt:"+c);
        
        String replace=name.replace("Abdul Mukit","Mukit ahmed");
        System.out.println("replace name:"+replace);
    }
    
}

string(CompareTo and indexOf)

package stringcompare;

public class StringCompare {

    
    public static void main(String[] args) {
        String myName="Bangladesh";
        String YourName="Africa";
        char c='k';
        
        System.out.println("Index of k from myName:"+myName.indexOf(c));
        System.out.println("Index of k from yourName:"+YourName.indexOf(c));
        
        int result=myName.compareTo(YourName);
        
        if(result>0){
            
            System.out.println("greater:"+result);
        }
        else if(result<0){
            System.out.println("less:"+result);
        }
        else if(result==0){
            System.out.println("Equal:"+result);
        }
    }
    
}

for loop and array

package arrayloop;
import java.util.Arrays;

public class Arrayloop {

    public static void main(String[] args) {
        int []arr={3,21,43,4,0};  
        int i;
        for(i=0;i<arr.length;i++){
            
            System.out.println(arr[i]);
        }
        Arrays.sort(arr);
        System.out.println("After sorting");
        
        for(i=0;i<arr.length;i++){
            
            System.out.println(arr[i]);
        }
    }
    
}

if else and switch case

import java.util.Scanner;
import java.lang.*;

class condition{

public static void main(String args[]){
char c;
Scanner in=new Scanner(System.in);
System.out.println("Please enter a positive negaive or zero");
c=in.next().charAt(0);

if(c=='+'){
System.out.println("This is positive character");
}
        else{
        switch(c){
        case '-':
        System.out.println("This is negative character");
        break;
        default:
        System.out.println("404 invalid input");
        }
         } 
   }
}

Taking User Input

import java.util.Scanner;
import java.lang.*;

class userinput{

    public static void main(String args[]){

    Scanner in=new Scanner(System.in);
    System.out.println("Please enter a Integer value:");
    int x=in.nextInt();
    System.out.println("Integer value: "+x);

    System.out.println("Please enter a character value:");
    char c=in.next().charAt(0);
    System.out.println("Character value: "+c);

    System.out.println("Please enter a float value:");
    float f=in.nextFloat();
    System.out.println("float value:"+f);

    System.out.println("Please enter a double value:");
    double d=in.nextDouble();
    System.out.println("Double value:"+d);

    System.out.println("Please enter a String value:");
    String str;
    str=in.nextLine();
    System.out.print("String Value:"+str);

    }

}

variable

class hello
{
    void add(Integer a,Integer b){
      Integer res=a+b;
 System.out.println(res);
   }
   
public static void main(String[] args)
{

byte a;
a=27;
System.out.println("BYTE: "+a);

short b;
b=1201;
System.out.println("SHORT: "+b);

int x;
x=13256;
System.out.println("INT: "+x);

long z;
z=236464;
System.out.println("LONG: "+z);

float f;
f=(float)23.25;
System.out.println("FLOAT: "+f);

double d;
d=54.12546;
System.out.println("Double: " +d);

char c;
c='J';
System.out.println("CHAR: "+c);

boolean k;
k=false;
System.out.println("BOOLEAN: "+k);
   
System.out.println(new Integer(10));

Integer j=new Integer(10);
j=2;
System.out.println(j);
Integer j2=100;///Integer j2=new Integer(100);
System.out.println(j2);
hello h=new hello();
h.add(j,j2);

}
}