if condition used with JOptionPane showMessageDialog - if-statement

Question

The code below when run generates only the name of the last student with marks<30 I want all the names of the student to be displayed in the same message dialog box. Please help. Thanks and I'm fairly new to coding.
import javax.swing.JOptionPane;
class marks
{
public static void main(String args[])
{
String name=" ";
int marks=0;
for(int x=0; x<3; x++)
{
name=JOptionPane.showInputDialog(null,"Please enter the name");
marks=Integer.parseInt(JOptionPane.showInputDialog(null,"Please enter the marks"));
}
if (marks<30)
{
(JOptionPane.showMessageDialog(null,"the students who got marks below 30 are: "+name));
}
}
}

Answer 1

I think you need to read some basics. Also for that purposes use arrays instead of one variable. I change your code, I think it do what you want :
public class marks {
public static void main(String args[]) {
int count = 3;
String[] name = new String[3];
int[] marks = new int[3];
for (int x = 0; x < count; x++) {
name[x] = JOptionPane.showInputDialog(null, "Please enter the name");
marks[x] = Integer.parseInt(JOptionPane.showInputDialog(null,"Please enter the marks"));
}
String names="";
for(int i = 0;i<count;i++){
if (marks[i] < 30){
names+= name[i]+", ";
}
}
if(names.endsWith(", ")){
names = names.substring(0,names.length()-2);
}
if(!names.isEmpty()){
JOptionPane.showMessageDialog(null,"the students who got marks below 30 are: " + names);
}
}
}

Answer 2

import java.util.ArrayList;
import javax.swing.JList;
import javax.swing.JOptionPane;
import javax.swing.JScrollPane;
class marks
{
public static void main(String args[])
{int x=0;
// String name=" ";
// int marks=0;
ArrayList<Integer> marks= new ArrayList<Integer>();
ArrayList<String> name= new ArrayList<String>();
ArrayList<String> array = new ArrayList<String>();
for(x=0; x<3; x++)
{
name.add(JOptionPane.showInputDialog(null,"Please enter the name"));
marks.add(Integer.parseInt(JOptionPane.showInputDialog(null,"Please enter the marks")));
}
// if (marks<30)
for(x=0 ; x<name.size(); x++)
{
if(marks.get(x)<30){
array.add(name.toString());
// JOptionPane.showMessageDialog(null,"the students who got marks below 30 are: "+name.);
break;
}
}
JOptionPane.showMessageDialog(null, new JScrollPane(new JList(array.toArray())));
}
}