What's the difference between "JDK" and "JRE"?

[broli]

It seems both have a java.exe which can be used to execute the byte
code(.class) but then jre does not have the javac compiler.

 

[Sabine Dinis Blochberger]

It seems both have a java.exe which can be used to execute the byte
code(.class) but then jre does not have the javac compiler.

You basically answered your own question.

 

[Andrea Francia]

It seems both have a java.exe which can be used to execute the byte
code(.class) but then jre does not have the javac compiler.

Google is your friend
http://www.google.com/search?q=jre+jdk+difference

 

[Roedy Green]

It seems both have a java.exe which can be used to execute the byte
code(.class) but then jre does not have the javac compiler.

see http://mindprod.com/jgloss/jre.html
http://mindprod.com/jgloss/jdk.html

You need the JDK if you want to write your own programs. If you just
want to run them, you can get away with the JRE.

 

[Mark Space]

It seems both have a java.exe which can be used to execute the byte
code(.class) but then jre does not have the javac compiler.

Pretty much that is it. There are more development tools in the JDK
than just javac, but that's the idea. JRE is just the runtime, for a
user who wants to only run programs other write. The JDK is for
programmers who need more tools, like javac.

 

[Arne Vajhøj]

Pretty much that is it. There are more development tools in the JDK
than just javac, but that's the idea. JRE is just the runtime, for a
user who wants to only run programs other write. The JDK is for
programmers who need more tools, like javac.

It should be noted though that a few server products requires
the JDK just for running, because they use stuff from tools.jar.

Arne

 

[Roedy Green]

It should be noted though that a few server products requires
the JDK just for running, because they use stuff from tools.jar.

Java.exe -server lives in the JDK only.

 

[Arne Vajhøj]

Java.exe -server lives in the JDK only.

1) No.

C:\Program Files\Java\jre1.6.0\bin>java -?
Usage: java [-options] class [args...]
(to execute a class)
or java [-options] -jar jarfile [args...]
(to execute a jar file)

where options include:
-client to select the "client" VM
-server to select the "server" VM

2) Even though most server apps uses the server VM, then it
is perfectly valid to use server VM for client apps and client
VM for server apps.

Arne

 

[Roedy Green]

1) No.

A while a go I did benchmarks with client and server. I found that the
JRE version of java.exe did not understand -server.

the system32 version of java.exe might be smart enough to use the JDK
version if you use -server.

 

[Arne Vajhøj]

A while a go I did benchmarks with client and server. I found that the
JRE version of java.exe did not understand -server.

the system32 version of java.exe might be smart enough to use the JDK
version if you use -server.

As I showed then in the stuff you did not quote, then the java.exe
in my JRE does understand (or at least claim to) -server.

It is also very simple to use fc to verify that the java.exe in the
JRE bin and the JDK bin are identical.

Arne

 

[Roedy Green]

It is also very simple to use fc to verify that the java.exe in the
JRE bin and the JDK bin are identical.

that means little. They look in the registry ,load dlls, figure out
which JDK/JRE to use etc. So the exact same executable can behave
differently in different contexts.

The most obvious example would be using an java.exe in a JRE uses that
JRE where the one in system32 looks in the registry ot decide which
JRE to use then loads that one.

 

[Roedy Green]

As I showed then in the stuff you did not quote, then the java.exe
in my JRE does understand (or at least claim to) -server.

I just did an experiment


[F:\Program Files\Java\jdk1.6.0_05\jre\bin]java -server -jar
E:\com\mindprod\converter\converter.jar

which would have used the jre java.exe and it worked happily. You are
correct. Now the question is, is this behaviour new in 1.6, or was it
always thus and something threw me off earlier.

 

[Arne Vajhøj]

As I showed then in the stuff you did not quote, then the java.exe
in my JRE does understand (or at least claim to) -server.

I just did an experiment


[F:\Program Files\Java\jdk1.6.0_05\jre\bin]java -server -jar
E:\com\mindprod\converter\converter.jar

which would have used the jre java.exe and it worked happily. You are
correct. Now the question is, is this behaviour new in 1.6, or was it
always thus and something threw me off earlier.

C:\Program Files\Java\jre1.5.0\bin>java -?
Usage: java [-options] class [args...]
(to execute a class)
or java [-options] -jar jarfile [args...]
(to execute a jar file)

where options include:
-client to select the "client" VM
-server to select the "server" VM

C:\Program Files\Java\j2re1.4.2_02\bin>java -?
Usage: java [-options] class [args...]
(to execute a class)
or java [-options] -jar jarfile [args...]
(to execute a jar file)

where options include:
-client to select the "client" VM
-server to select the "server" VM

C:\Program Files\Java\j2re1.4.1_02\bin>java -?
Usage: java [-options] class [args...]
(to execute a class)
or java -jar [-options] jarfile [args...]
(to execute a jar file)

where options include:
-client to select the "client" VM
-server to select the "server" VM

Arne