Translate this C++ code into java code

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Java

#include<fstream.h>
#include<iostream.h>
#include<conio.h>
#include<stdlib.h>
#include<string.h>
fstream infile,outfile;
char source[20],dest[20];
void fileopen(fstream &file, char *fn, int mode)
{
file.open(fn,mode);
if(!file)
{
cout<<"file doesnot exit";
getch();
exit(0);
}
}
void readfilename()
{
cout<<"enter the source to perform encrpyt/decrypt the file:";
cin>>source;
fileopen(infile,source,ios::in|ios::binary);
cout<<"enter the destination file to store encrypt/decrypted file:";
cin>>dest;
fileopen(outfile,dest,ios::out|ios::binary);
}

void subecn()
{
char ch;
readfilename();
while(infile)
{
infile.get(ch);
if(infile)
outfile.put(ch+1);
}
}
void subdecr()
{
char ch;
readfilename();
while(infile)
{
infile.get(ch);
if(infile)
outfile.put(ch-1);
}
}
void tranecn()
{
char ch,*buff,*str1,*str2;
int i=0,j=0,k=0;
readfilename();
while(infile)
{
infile.get(ch);
if(infile)
buff[i++]=ch;
}
buff[i]='\0';
str1=(char *)malloc(strlen(buff)/2+1);
str2=(char *)malloc(strlen(buff)/2+1);
for(i=0;i<strlen(buff);i++)>
if(i%2==0)
str1[j++]=buff[i];
else
str2[k++]=buff[i];
str1[j]='\0';
str2[k]='\0';
outfile<<str1<<str2;
}
void trandecr()
{
char ch,*buff,*str1,*str2;
int i=0,j=0,mid;
readfilename();
while(infile)
{
infile.get(ch);
if(infile)
buff[i++]=ch;
}
buff[i]='\0';
cout<<buff;
if(strlen(buff)%2==0)
mid=strlen(buff)/2;
else
mid = strlen(buff)/2+1;
str1=(char *)malloc(mid+1);
str2=(char *)malloc(mid+1);
strncpy(str1,buff,mid);
for(i=mid;i<strlen(buff);i++)>
str2[j++]=buff[i];
str1[mid]='\0';
str2[j]='\0';
for(i=0;i<mid;i++)>
outfile<<str1[i]<<str2[i];
}
int main()
{
int choice;
while(1)
{
cout<<"1 sub encr, 2 sub decr, 3 tran encr 4 tran decr, 5 exit\n";
cin>>choice;
switch(choice)
{
case 1: subecn();
break;
case 2: subdecr();
break;
case 3: tranecn();
break;
case 4: trandecr();
break;
case 5: return 0;
}
infile.close();
outfile.close();
}
}