Reputation: 5
java if statement string comparison
package canlitahmin;
import java.sql.*;
import java.util.ArrayList;
import java.util.List;
public class baglanti {
// JDBC driver name and database URL
static final String JDBC_DRIVER = "com.mysql.jdbc.Driver";
static final String DB_URL = "jdbc:mysql://localhost:3306/canlitahmin";
// Database credentials
static final String USER = "root";
static final String PASS = "";
public static List<Integer> id = new ArrayList<Integer>();
public static List<Integer> evgol = new ArrayList<Integer>();
public static List<Integer> kuralid = new ArrayList<Integer>();
public static List<String> kural = new ArrayList<String>();
public static List<Integer> depgol = new ArrayList<Integer>();
public static List<Integer> dakika = new ArrayList<Integer>();
public static void main(String[] args) {
Connection conn = null;
Statement stmt = null;
Statement stmt2 = null;
try{
//STEP 2: Register JDBC driver
Class.forName("com.mysql.jdbc.Driver");
//STEP 3: Open a connection
System.out.println("Connecting to database...");
conn = DriverManager.getConnection(DB_URL,USER,PASS);
//STEP 4: Execute a query
System.out.println("Creating statement...");
stmt = conn.createStatement();
stmt2 = conn.createStatement();
String sql;
String sql2;
sql = "SELECT id, evgol, depgol, dk FROM maclar";
sql2="SELECT id,kural from kurallar";
ResultSet rs = stmt.executeQuery(sql);
ResultSet rs2 = stmt2.executeQuery(sql2);
int i=0;
//STEP 5: Extract data from result set
while(rs.next()){
//Retrieve by column name
id.add(rs.getInt("id"));
evgol.add(rs.getInt("evgol"));
depgol.add(rs.getInt("depgol"));
dakika.add(rs.getInt("dk"));
//Display values
System.out.print("ID: " + id.get(i));
System.out.print(", Evgol: " + evgol.get(i));
System.out.print(", Depgol: " + depgol.get(i));
System.out.println(", dakika: " + dakika.get(i));
i++;
}
int k=0;
while(rs2.next()){
//Retrieve by column name
kuralid.add(rs2.getInt("id"));
kural.add(rs2.getString("kural"));
//Display values
System.out.print("KURALID: " + kuralid.get(k));
System.out.println(", KURAL: " + kural.get(k));
k++;
}
for(int l=0;l<id.size();l++){
int BYTG=evgol.get(l);
int DEPTG=depgol.get(l);
/* int DK=dakika.get(l);
int MACKODLARI=id.get(l);*/
for(int j=0;j<kuralid.size();j++){
###if(kural.get(j))###{ // ERROR**********************************
double a=BYTG+DEPTG+0.5;
int b=BYTG+DEPTG;
String kural="Tahmin:"+a+" üstü ve "+b+" üstü";
System.out.println(kural);
}}
}
//STEP 6: Clean-up environment
rs.close();
rs2.close();
stmt.close();
stmt2.close();
conn.close();
}catch(SQLException se){
//Handle errors for JDBC
se.printStackTrace();
}catch(Exception e){
//Handle errors for Class.forName
e.printStackTrace();
}finally{
//finally block used to close resources
try{
if(stmt!=null)
stmt.close();
}catch(SQLException se2){
}// nothing we can do
try{
if(conn!=null)
conn.close();
}catch(SQLException se){
se.printStackTrace();
}//end finally try
}//end try
System.out.println("Goodbye!");
}//end main
}//end FirstExample
java if statement string comparison. my database datas get in "kural.get(j)" but kural.get(j) error. because its string variable. Question: String a=b>0 && c>0 -- if(a) how i use? String code in if with variable
Upvotes: 0
Views: 417
Answers (4)
Reputation: 37645
You cannot easily do that with Strings. What you can do is make an interface like this
interface IntIntPredicate {
public boolean test(int i, int j);
}
Then you can do (in Java 8):
IntIntPredicate a = (i, j) -> i == 1 && j <= 2;
IntIntPredicate b = (i, j) -> i <= 0 && j == 2;
Then later you can do:
if (a.test(i, j)) {
// do something
} else if (b.test(i, j)) {
// do something else
}
This is possible in earlier versions of Java, but the syntax is more clumsy.
If it is necessary for the data to be entered as a String, it would probably not be too difficult to write a method to parse a String (treating i and j as the first and second arguments) and return an IntIntPredicate
public static IntIntPredicate parse(String x) {
// This is going to require a lot of work, but
// there are many questions on this site about how
// to parse expressions such as "(2 + 3) * 9"
}
Upvotes: 1
Reputation: 2098
You can also used ScriptEngine, but you need to translate the logic to a scripting language like Javascript.
import javax.script.ScriptEngineManager;
import javax.script.ScriptEngine;
import javax.script.ScriptException;
/**
*
* @author afshin
*/
public class Blah {
/**
* @param args the command line arguments
*/
public static void main(String[] args) throws ScriptException {
ScriptEngineManager mgr = new ScriptEngineManager();
ScriptEngine engine = mgr.getEngineByName("JavaScript");
int i = 1;
int j = 1;
String a = i + "==1 && " + j +"<=2";
String b= i + "<=0 && " + j+"==2";
if (((Boolean) engine.eval(a)))
System.out.println("a is true");
if (((Boolean) engine.eval(b)))
System.out.println("b is true");
}
}
Upvotes: 0
Reputation: 190
You could make a method, like:
boolean predicate(i,j) {
if (i==1 and j <=2) {
return true;
}
return false;
}
And then invoke the method like this:
if (predicate(i,j)) {
System.out.println("a");
}
Upvotes: 0
Reputation: 904
This can be done programmatically with the JavaCompiler and the javax.tools package
As a related question, see How do I programmatically compile and instantiate a Java class?
The solution is the same.
Upvotes: 1