Here is an example where we have created a function that accepts a string and an integer value and perform a upper case and lowercase method to the string.

import java.util.*;
class FunctionExample 
{
    void display(String str,int p){
        if(p==1){
            System.out.println(str.toUpperCase());
        }
        else{
            System.out.println(str.toLowerCase());
        }
    }

    public static void main(String[] args) 
    {
        Scanner input=new Scanner(System.in);
        System.out.print("Enter string: ");
        String st=input.next();
        System.out.print("Enter integer: ");
        int i=input.nextInt();
        FunctionExample f=new FunctionExample();
        f.display(st,i);
    }
}

Here is an example where we have created a function that accepts a string and a character value.

import java.util.*;
class FunctionExample 
{
    void display(String str,char chr){
        if(chr=='v'){
                String vowels = "aeiouAEIOU";
                String res="";
                for( int i = 0; i < str.length(); i++ )
                if( vowels.indexOf( str.charAt( i ) ) != -1 )
                res=res+str.charAt( i );
            System.out.println("Vowels are: "+res);
        }
    }

    public static void main(String[] args) 
    {
        Scanner input=new Scanner(System.in);
        System.out.print("Enter string: ");
        String st=input.next();
        System.out.print("Enter character: ");
        char ch=input.next().charAt(0);
        FunctionExample f=new FunctionExample();
        f.display(st,ch);
    }
}