Mixing
Java Scanner returning null but already filtered out
public void process() throws InputMismatchException {
//System.out.println(code);
if(sc.findInLine("JP++") == null || sc.findInLine("START") == null){
throw new RuntimeException("Program has to start with 'JP++ _NAME_ START' ");
}
sc.nextLine();
while(sc.hasNext()){
if (sc.findInLine(Pattern.compile("JP......")) != "JP++ END" ){
Scanner r = sc;
if(!r.hasNextLine() || r.findInLine(Pattern.compile(".")) == null){
return;
}
System.out.println(sc.nextLine());
}
}
}
This code is a part of a lexer I am currently working on. I already filtered out to prevent the scanner from outputting null and it still output:
hello
world
null
my input: " JP++ HELLO WORLD START n hello n worldn JP++ END"
How can I solve this thx
java lexer
asked Nov 19 '18 at 14:25
Clement Hui
31
add a comment |
public void process() throws InputMismatchException {
//System.out.println(code);
if(sc.findInLine("JP++") == null || sc.findInLine("START") == null){
throw new RuntimeException("Program has to start with 'JP++ _NAME_ START' ");
}
sc.nextLine();
while(sc.hasNext()){
if (sc.findInLine(Pattern.compile("JP......")) != "JP++ END" ){
Scanner r = sc;
if(!r.hasNextLine() || r.findInLine(Pattern.compile(".")) == null){
return;
}
System.out.println(sc.nextLine());
}
}
}
This code is a part of a lexer I am currently working on. I already filtered out to prevent the scanner from outputting null and it still output:
hello
world
null
my input: " JP++ HELLO WORLD START n hello n worldn JP++ END"
How can I solve this thx
java lexer
asked Nov 19 '18 at 14:25
Clement Hui
31
... != "JP++ END"-> How do I compare strings in Java?
– Pshemo
Nov 19 '18 at 16:00
add a comment |
public void process() throws InputMismatchException {
//System.out.println(code);
if(sc.findInLine("JP++") == null || sc.findInLine("START") == null){
throw new RuntimeException("Program has to start with 'JP++ _NAME_ START' ");
}
sc.nextLine();
while(sc.hasNext()){
if (sc.findInLine(Pattern.compile("JP......")) != "JP++ END" ){
Scanner r = sc;
if(!r.hasNextLine() || r.findInLine(Pattern.compile(".")) == null){
return;
}
System.out.println(sc.nextLine());
}
}
}
This code is a part of a lexer I am currently working on. I already filtered out to prevent the scanner from outputting null and it still output:
hello
world
null
my input: " JP++ HELLO WORLD START n hello n worldn JP++ END"
How can I solve this thx
java lexer
asked Nov 19 '18 at 14:25
Clement Hui
31
public void process() throws InputMismatchException {
//System.out.println(code);
if(sc.findInLine("JP++") == null || sc.findInLine("START") == null){
throw new RuntimeException("Program has to start with 'JP++ _NAME_ START' ");
}
sc.nextLine();
while(sc.hasNext()){
if (sc.findInLine(Pattern.compile("JP......")) != "JP++ END" ){
Scanner r = sc;
if(!r.hasNextLine() || r.findInLine(Pattern.compile(".")) == null){
return;
}
System.out.println(sc.nextLine());
}
}
}
This code is a part of a lexer I am currently working on. I already filtered out to prevent the scanner from outputting null and it still output:
hello
world
null
my input: " JP++ HELLO WORLD START n hello n worldn JP++ END"
How can I solve this thx
java lexer
java lexer
asked Nov 19 '18 at 14:25
Clement Hui
31
asked Nov 19 '18 at 14:25
Clement Hui
31
asked Nov 19 '18 at 14:25
Clement Hui
31
asked Nov 19 '18 at 14:25
Clement Hui
31
asked Nov 19 '18 at 14:25
Clement Hui
31
31
... != "JP++ END"-> How do I compare strings in Java?
– Pshemo
Nov 19 '18 at 16:00
add a comment |
... != "JP++ END"-> How do I compare strings in Java?
– Pshemo
Nov 19 '18 at 16:00
... != "JP++ END" -> How do I compare strings in Java?– Pshemo
Nov 19 '18 at 16:00
... != "JP++ END" -> How do I compare strings in Java?– Pshemo
Nov 19 '18 at 16:00
add a comment |
1 Answer
1
active
oldest
votes
I just tested this code :
String input = " JP++ HELLO WORLD START n hello n worldn JP++ END";
Scanner sc = new Scanner(input);
if(sc.findInLine("JP++") == null || sc.findInLine("START") == null){
throw new RuntimeException("Program has to start with 'JP++ _NAME_ START' ");
}
sc.nextLine();
while(sc.hasNext()){
if (sc.findInLine(Pattern.compile("JP......")) != "JP++ END" ) {
Scanner r = sc;
if(!r.hasNextLine() || r.findInLine(Pattern.compile(".")) == null){
return;
}
System.out.println(sc.nextLine());
}
}
Which is literally a copy and paste of your code except for the input (which I also literally copied from your post) and Scanner declaration. It prints out
hello
world
with no null. Whatever your issue is it is elsewhere.
Edit : As @Pshemo mentions you are also comparing your string wrong. Use .equals()
answered Nov 19 '18 at 14:55
John Kim
413211
Thank you very much. Many thanks on your help
– Clement Hui
Nov 20 '18 at 12:34
add a comment |
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1 Answer
1
active
oldest
votes
1 Answer
1
active
oldest
votes
active
oldest
votes
active
oldest
votes
I just tested this code :
String input = " JP++ HELLO WORLD START n hello n worldn JP++ END";
Scanner sc = new Scanner(input);
if(sc.findInLine("JP++") == null || sc.findInLine("START") == null){
throw new RuntimeException("Program has to start with 'JP++ _NAME_ START' ");
}
sc.nextLine();
while(sc.hasNext()){
if (sc.findInLine(Pattern.compile("JP......")) != "JP++ END" ) {
Scanner r = sc;
if(!r.hasNextLine() || r.findInLine(Pattern.compile(".")) == null){
return;
}
System.out.println(sc.nextLine());
}
}
Which is literally a copy and paste of your code except for the input (which I also literally copied from your post) and Scanner declaration. It prints out
hello
world
with no null. Whatever your issue is it is elsewhere.
Edit : As @Pshemo mentions you are also comparing your string wrong. Use .equals()
answered Nov 19 '18 at 14:55
John Kim
413211
Thank you very much. Many thanks on your help
– Clement Hui
Nov 20 '18 at 12:34
add a comment |
I just tested this code :
String input = " JP++ HELLO WORLD START n hello n worldn JP++ END";
Scanner sc = new Scanner(input);
if(sc.findInLine("JP++") == null || sc.findInLine("START") == null){
throw new RuntimeException("Program has to start with 'JP++ _NAME_ START' ");
}
sc.nextLine();
while(sc.hasNext()){
if (sc.findInLine(Pattern.compile("JP......")) != "JP++ END" ) {
Scanner r = sc;
if(!r.hasNextLine() || r.findInLine(Pattern.compile(".")) == null){
return;
}
System.out.println(sc.nextLine());
}
}
Which is literally a copy and paste of your code except for the input (which I also literally copied from your post) and Scanner declaration. It prints out
hello
world
with no null. Whatever your issue is it is elsewhere.
Edit : As @Pshemo mentions you are also comparing your string wrong. Use .equals()
answered Nov 19 '18 at 14:55
John Kim
413211
Thank you very much. Many thanks on your help
– Clement Hui
Nov 20 '18 at 12:34
add a comment |
I just tested this code :
String input = " JP++ HELLO WORLD START n hello n worldn JP++ END";
Scanner sc = new Scanner(input);
if(sc.findInLine("JP++") == null || sc.findInLine("START") == null){
throw new RuntimeException("Program has to start with 'JP++ _NAME_ START' ");
}
sc.nextLine();
while(sc.hasNext()){
if (sc.findInLine(Pattern.compile("JP......")) != "JP++ END" ) {
Scanner r = sc;
if(!r.hasNextLine() || r.findInLine(Pattern.compile(".")) == null){
return;
}
System.out.println(sc.nextLine());
}
}
Which is literally a copy and paste of your code except for the input (which I also literally copied from your post) and Scanner declaration. It prints out
hello
world
with no null. Whatever your issue is it is elsewhere.
Edit : As @Pshemo mentions you are also comparing your string wrong. Use .equals()
answered Nov 19 '18 at 14:55
John Kim
413211
I just tested this code :
String input = " JP++ HELLO WORLD START n hello n worldn JP++ END";
Scanner sc = new Scanner(input);
if(sc.findInLine("JP++") == null || sc.findInLine("START") == null){
throw new RuntimeException("Program has to start with 'JP++ _NAME_ START' ");
}
sc.nextLine();
while(sc.hasNext()){
if (sc.findInLine(Pattern.compile("JP......")) != "JP++ END" ) {
Scanner r = sc;
if(!r.hasNextLine() || r.findInLine(Pattern.compile(".")) == null){
return;
}
System.out.println(sc.nextLine());
}
}
Which is literally a copy and paste of your code except for the input (which I also literally copied from your post) and Scanner declaration. It prints out
hello
world
with no null. Whatever your issue is it is elsewhere.
Edit : As @Pshemo mentions you are also comparing your string wrong. Use .equals()
answered Nov 19 '18 at 14:55
John Kim
413211
edited Nov 19 '18 at 16:08
answered Nov 19 '18 at 14:55
John Kim
413211
answered Nov 19 '18 at 14:55
John Kim
413211
answered Nov 19 '18 at 14:55
John Kim
413211
413211
Thank you very much. Many thanks on your help
– Clement Hui
Nov 20 '18 at 12:34
add a comment |
Thank you very much. Many thanks on your help
– Clement Hui
Nov 20 '18 at 12:34
Thank you very much. Many thanks on your help
– Clement Hui
Nov 20 '18 at 12:34
Thank you very much. Many thanks on your help
– Clement Hui
Nov 20 '18 at 12:34
add a comment |
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... != "JP++ END"-> How do I compare strings in Java?– Pshemo
Nov 19 '18 at 16:00