how to form clusters of number pairs using java

hi guys i am writing a program where it takes number pairs as input and form the clusters based on the common numbers between the pairs.This is the code i have written so far:

public class cluster 
{ 
public static void main(String args[]) throws FileNotFoundException 
{ ArrayList<arraylist><integer>> x = new ArrayList(); 
ArrayList y = new ArrayList(); 
ArrayList k=new ArrayList(); 
ArrayList z=new ArrayList(); 
ArrayList w=new ArrayList(); 

System.out.println("how many"); 
Scanner s=new Scanner(System.in); 
int n=s.nextInt(); 
for(int i=1;i<=n;i++) 
{ 
System.out.println("enter pairs"); 
int a=s.nextInt(); 
int b=s.nextInt(); 
if(!y.contains(a) && !y.contains(b)&& x.isEmpty()) 
{ y.add(a); 
y.add(b); 

x.add(y); 
System.out.println(y); 
} 
else if(!y.contains(a) && !y.contains(b)&& !x.isEmpty() && k.isEmpty()) 
{ 

k.add(a); 
k.add(b); 
System.out.println(k); 
System.out.println(y); 

} 

else if(!y.contains(a) && !y.contains(b)&& !x.isEmpty() && !k.isEmpty() && z.isEmpty()) 
{ 
if(k.contains(a)&& !k.contains(b)) 
{ 
k.add(b); 

System.out.println(k); 

} 
else if(!k.contains(a)&& k.contains(b)) 
{ 
k.add(a); 
System.out.println(k); 
System.out.println(y); 

} 
else if(!k.contains(a)&& !k.contains(b)) 
{ 
z.add(a); 
z.add(b); 
System.out.println(z); 
System.out.println(k); 
System.out.println(k); 

} 

} 
else if(!y.contains(a) && !y.contains(b)&& !x.isEmpty() && !k.isEmpty() && !z.isEmpty()) 
{ 
if(z.contains(a)&& !z.contains(b)) 
{ 
z.add(b); 
System.out.println(z); 
} 
else if(!z.contains(a)&& z.contains(b)) 
{ 
z.add(a); 
System.out.println(z); 

} 
else if(!z.contains(b) && !z.contains(a)) 
{ 
w.add(a); 
w.add(b); 
System.out.println(w); 
} } 

Now what my problem is if i am entering 5 distinct pairs i am able to get 4 distinct clusters but if my 5th pair is also a unique pair then my 5th pair is added to the 4th pair forming that as cluster.How can i write nested if loops if there are 1000 pairs .please guys help me how to make this code work even for 1000 pairs

Input: 
1 2 
2 4 
3 5 
6 7 
8 9 
11 12 
Expected output: 
1 2 4 
3 5 
6 7 
8 9 
11 12 
My output: 
1 2 4 
3 5 
6 7 
8 9 11 12

Tags: Java