This section provides a tutorial example on how to use the '-classpath' option to specify the class path for the 'java' tool to load any classes required during the execution.
The most commonly used "java" option is "-classpath", which specifies a list of path names
where the launcher will search for compiled type definitions.
If "-classpath" is not specified, the current directory will be used as the class path.
To experiment how the compiler uses "-classpath", I wrote the following simple source file, Echoer.java:
/**
* Echoer.java
* Copyright (c) 2006 by Dr. Herong Yang, http://www.herongyang.com/
*/
public class Echoer {
private String req = null;
private String res = null;
public void setReq(String r) {
req = new String(r);
char[] a = r.toCharArray();
int n = a.length;
for (int i=0; i<n/2; i++) {
char t = a[i];
a[i] = a[n-1-i];
a[n-i-1] = t;
}
res = new String(a);
}
public String getRes() {
return res;
}
}
I also wrote the following testing class, EchoerTest.java:
/**
* EchoerTest.java
* Copyright (c) 2006 by Dr. Herong Yang, http://www.herongyang.com/
*/
public class EchoerTest {
public static void main(String[] a) {
Echoer e = new Echoer();
e.setReq("Hello world!");
System.out.println(e.getRes());
}
}
Then I stored them in two different directories, and tried to launch EchoerTest:
C:\herong>mkdir echo
C:\herong>copy Echoer.java echo
C:\herong>mkdir test
C:\herong>copy EchoerTest.java test
C:\herong>cd test
C:\herong>javac -classpath ..\echo EchoerTest.java
>java EchoerTest
Exception in thread "main" java.lang.NoClassDefFoundError: Echoer
at EchoerTest.main(EchoerTest.java:7)
C:\herong>java -classpath ..\echo EchoerTest
Exception in thread "main" java.lang.NoClassDefFoundError: EchoerTest
C:\herong>java -classpath .;..\echo EchoerTest
!dlrow olleH
Note that:
The first time I tried to launch "EchoerTest" without "-classpath", "java" failed to find "Echoer" class,
because "java" uses the current directory as the default class path.
The second time I tried to launch "EchoerTest" with "-classpath ..\echo", "java" failed to find "EchoerTest" class,
because the specified class path didn't include the current directory.
The third time I tried to launch "EchoerTest" with "-classpath .;..\echo", "java" was able to find both
"EchoerTest" and "Echoer".
