Javascript – Convert Number to int? incompatible types found : void required: int

google mapsjavajavascriptjsp

I am writing an application to get latitude, longitude of a position in a google map using java and javascript.

The below code part gives an error:

code(It's a part of a jsp file):

<script type="text/javascript">
  var map;

  //Initialization & some more code goes here

  function centerChanged() {
    <%
        int lat=0,lng=0;
        lat=%>map.getCenter().lat();<%
        lng=%>map.getCenter().lng();<%
        //request.setAttribute("lat", lat);
        //request.setAttribute("lng", lng);
    %>    
  }

From the above code, these are the two lines that cause the error:

    lat=%>map.getCenter().lat();<%
    lng=%>map.getCenter().lng();<%

Additional Information:

map.getCenter().lat() << This will return a Number as mentioned in google maps API:

This is the error I am getting:

org.apache.jasper.JasperException: PWC6033: Error in Javac compilation
for JSP

PWC6197: An error occurred at line: 81 in the jsp file: /maptest.jsp
PWC6199: Generated servlet error: string:///maptest_jsp.java:127:
incompatible types found : void required: int

PWC6197: An error occurred at line: 82 in the jsp file: /maptest.jsp
PWC6199: Generated servlet error: string:///maptest_jsp.java:130:
incompatible types found : void required: int

Can anyone please tell what is wrong?

Best Answer

You are trying to dynamically insert a value from Javascript into JSP. The mistake is that JSP is executed on the server side, whilst Javascript on client side.

What you wrote there is equal to Java code:

out.write("function centerChanged() {");
int lat=0,lng=0;
lat=;
out.write("map.getCenter().lat();");
lng=;
out.write("map.getCenter().lng();");
//request.setAttribute("lat", lat);
//request.setAttribute("lng", lng);
out.write("}");

Get it? Whatever is surrounded by <%%> is pure Java code, whatever is outside of it, is printed out, hence your exception.

To work around it, you need to change the logic how you retrieve the client-side Javascript values in your server-side JSP code.

Examples

Positive

// value=x        //  x=5          5<x<5.5      5.5<=x<6  

Math.floor(value) //  5            5            5
Math.ceil(value)  //  5            6            6
Math.round(value) //  5            5            6
Math.trunc(value) //  5            5            5
parseInt(value)   //  5            5            5
~~value           //  5            5            5
value | 0         //  5            5            5
value >> 0        //  5            5            5
value >>> 0       //  5            5            5
value - value % 1 //  5            5            5

Negative

// value=x        // x=-5         -5>x>=-5.5   -5.5>x>-6

Math.floor(value) // -5           -6           -6
Math.ceil(value)  // -5           -5           -5
Math.round(value) // -5           -5           -6
Math.trunc(value) // -5           -5           -5
parseInt(value)   // -5           -5           -5
value | 0         // -5           -5           -5
~~value           // -5           -5           -5
value >> 0        // -5           -5           -5
value >>> 0       // 4294967291   4294967291   4294967291
value - value % 1 // -5           -5           -5

Positive - Larger numbers

// x = Number.MAX_SAFE_INTEGER/10 // =900719925474099.1

// value=x            x=900719925474099    x=900719925474099.4  x=900719925474099.5
           
Math.floor(value) //  900719925474099      900719925474099      900719925474099
Math.ceil(value)  //  900719925474099      900719925474100      900719925474100
Math.round(value) //  900719925474099      900719925474099      900719925474100
Math.trunc(value) //  900719925474099      900719925474099      900719925474099
parseInt(value)   //  900719925474099      900719925474099      900719925474099
value | 0         //  858993459            858993459            858993459
~~value           //  858993459            858993459            858993459
value >> 0        //  858993459            858993459            858993459
value >>> 0       //  858993459            858993459            858993459
value - value % 1 //  900719925474099      900719925474099      900719925474099

Negative - Larger numbers

// x = Number.MAX_SAFE_INTEGER/10 * -1 // -900719925474099.1

// value = x      // x=-900719925474099   x=-900719925474099.5 x=-900719925474099.6

Math.floor(value) // -900719925474099     -900719925474100     -900719925474100
Math.ceil(value)  // -900719925474099     -900719925474099     -900719925474099
Math.round(value) // -900719925474099     -900719925474099     -900719925474100
Math.trunc(value) // -900719925474099     -900719925474099     -900719925474099
parseInt(value)   // -900719925474099     -900719925474099     -900719925474099
value | 0         // -858993459           -858993459           -858993459
~~value           // -858993459           -858993459           -858993459
value >> 0        // -858993459           -858993459           -858993459
value >>> 0       //  3435973837           3435973837           3435973837
value - value % 1 // -900719925474099     -900719925474099     -900719925474099

Java – How to convert a String to an int in Java

String myString = "1234";
int foo = Integer.parseInt(myString);

If you look at the Java documentation you'll notice the "catch" is that this function can throw a NumberFormatException, which of course you have to handle:

int foo;
try {
   foo = Integer.parseInt(myString);
}
catch (NumberFormatException e)
{
   foo = 0;
}

(This treatment defaults a malformed number to 0, but you can do something else if you like.)

Alternatively, you can use an Ints method from the Guava library, which in combination with Java 8's Optional, makes for a powerful and concise way to convert a string into an int:

import com.google.common.primitives.Ints;

int foo = Optional.ofNullable(myString)
 .map(Ints::tryParse)
 .orElse(0)

code(It's a part of a jsp file):

Additional Information:

This is the error I am getting:

Best Answer

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