Language: Java

import java.util.*;
public class Main{
        Scanner sc = new Scanner(System.in);
        StringBuilder sb = new StringBuilder();
        int sx =  Integer.parseInt(sc.next());
        int sy =  Integer.parseInt(sc.next());      
        int tx =  Integer.parseInt(sc.next());               
        int ty =  Integer.parseInt(sc.next());        
        int dx = tx - sx;
        int dy = ty - sy;
        for(int i = 0; i < dx; i++){
            sb.append('R');            
        } 
        for(int i = 0; i < dy; i++ ){ 
            sb.append('U');
        }
        for(int i = 0; i < dx; i++ ){
            sb.append('L');
        } 
        for(int i = 0; i < dy; i++){
            sb.append('D');
        }
        sb.append('D');
        for(int i = 0; i < dx+1; i++){
            sb.append('R');            
        }       
        for(int i = 0; i < dy+1; i++ ){ 
            sb.append('U');
        }
        sb.append('L');
        sb.append('U');
        for(int i = 0; i < dx+1; i++ ){
            sb.append('L');
        }        
        for(int i = 0; i < dy+1; i++){
            sb.append('D');
        } 
        sb.append('R'); 
        System.out.println(new String(sb));
 }

Compiler output:
Main.java:11: error: illegal start of type
        for(int i = 0; i < dx; i++){
        ^
Main.java:11: error: > or ',' expected
        for(int i = 0; i < dx; i++){
                             ^
Main.java:11: error: <identifier> expected
        for(int i = 0; i < dx; i++){
                                ^
Main.java:14: error: illegal start of type
        for(int i = 0; i < dy; i++ ){ 
        ^
Main.java:14: error: > or ',' expected
        for(int i = 0; i < dy; i++ ){ 
                             ^
Main.java:14: error: <identifier> expected
        for(int i = 0; i < dy; i++ ){ 
                                ^
Main.java:17: error: illegal start of type
        for(int i = 0; i < dx; i++ ){
        ^
Main.java:17: error: > or ',' expected
        for(int i = 0; i < dx; i++ ){
                             ^
Main.java:17: error: <identifier> expected
        for(int i = 0; i < dx; i++ ){
                                ^
Main.java:20: error: illegal start of type
        for(int i = 0; i < dy; i++){
        ^
Main.java:20: error: > or ',' expected
        for(int i = 0; i < dy; i++){
                             ^
Main.java:20: error: <identifier> expected
        for(int i = 0; i < dy; i++){
                                ^
Main.java:23: error: <identifier> expected
        sb.append('D');
                 ^
Main.java:23: error: illegal start of type
        sb.append('D');
                  ^
Main.java:24: error: illegal start of type
        for(int i = 0; i < dx+1; i++){
        ^
Main.java:24: error: > or ',' expected
        for(int i = 0; i < dx+1; i++){
                             ^
Main.java:24: error: <identifier> expected
        for(int i = 0; i < dx+1; i++){
                                  ^
Main.java:27: error: illegal start of type
        for(int i = 0; i < dy+1; i++ ){ 
        ^
Main.java:27: error: > or ',' expected
        for(int i = 0; i < dy+1; i++ ){ 
                             ^
Main.java:27: error: <identifier> expected
        for(int i = 0; i < dy+1; i++ ){ 
                                  ^
Main.java:30: error: <identifier> expected
        sb.append('L');
                 ^
Main.java:30: error: illegal start of type
        sb.append('L');
                  ^
Main.java:31: error: <identifier> expected
        sb.append('U');
                 ^
Main.java:31: error: illegal start of type
        sb.append('U');
                  ^
Main.java:32: error: illegal start of type
        for(int i = 0; i < dx+1; i++ ){
        ^
Main.java:32: error: > or ',' expected
        for(int i = 0; i < dx+1; i++ ){
                             ^
Main.java:32: error: <identifier> expected
        for(int i = 0; i < dx+1; i++ ){
                                  ^
Main.java:35: error: illegal start of type
        for(int i = 0; i < dy+1; i++){
        ^
Main.java:35: error: > or ',' expected
        for(int i = 0; i < dy+1; i++){
                             ^
Main.java:35: error: <identifier> expected
        for(int i = 0; i < dy+1; i++){
                                  ^
Main.java:38: error: <identifier> expected
        sb.append('R'); 
                 ^
Main.java:38: error: illegal start of type
        sb.append('R'); 
                  ^
Main.java:39: error: <identifier> expected
        System.out.println(new String(sb));
                          ^
Main.java:39: error: illegal start of type
        System.out.println(new String(sb));
                           ^
34 errors