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Hi ,
I have a String from the database which will hold symbols + - etc. In the java code I should use this string as a operator to evaluate an expression like , say A + B = C
where the plus sign is to be substituted by the String from DB..How do I accomplish this in Java...Any methods to parse Strings into arithmetic operators ?? Any help is highly appreciated.
Thanks,
Rajesh
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There are no such methods. There is no mechanism to convert a String to an operator. You will need to code if/switch blocks
if (string.equals("+")) {
do addtion
etc
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There are no such methods. There is no mechanism to convert a String to an operator. You will need to code if/switch blocks
if (string.equals("+")) {
do addtion
etc
There
are methods for this.
Say, you have the String:
String value = "A + B = C";
and you want to replace + sign with "plus" word for example.
value.replaceAll("+", "plus");
this feature came with Java 1.4
Regards
Onur.
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If you are able to use Java 5, you can try something like this...
(It's far from a complete implementation, but it will point you in the right direction - feel free to give feedback/improve the code as you see fit)
------------------
import java.util.HashMap;
import java.util.Map;
public enum Operation{
PLUS("+"){
public double execute(double a, double b){
return a + b;
}
},
MINUS("-"){
public double execute(double a, double b){
return a - b;
}
},
TIMES("*"){
public double execute(double a, double b){
return a * b;
}
},
DIVIDE("/"){
public double execute(double a, double b){
return a / b;
}
};
private String symbol;
private static final Map map = new HashMap();
static{
for (Operation operation : Operation.values()) {
map.put(operation.getSymbol(), operation);
}
}
private Operation(String symbol){
this.symbol = symbol;
}
public String getSymbol() {
return symbol;
}
public abstract double execute(double a, double b);
public static double apply(String symbol, double a, double b){
Operation operation = map.get(symbol);
if(operation != null){
return operation.execute(a,b);
}
throw new UnsupportedOperationException("No operation support for symbol '" + symbol + "'");
}
}
------------------------
And the test case for it
------------------------
import junit.framework.TestCase;
public class TestOperation extends TestCase {
public void testPlus(){
assertEquals(4.0, Operation.apply("+", 3, 1));
}
public void testMinus(){
assertEquals(2.0, Operation.apply("-", 3, 1));
}
public void testTimes(){
assertEquals(3.0, Operation.apply("*", 3, 1));
}
public void testDivide(){
assertEquals(3.0, Operation.apply("/", 3, 1));
}
public void testUnsupported(){
try{
Operation.apply("?", 3, 1);
fail("This operation should throw an UnsupportedOperationException");
}
catch(UnsupportedOperationException e){
//do nothing = we expect to get here
}
}
}
