Java 5.0 and 6 used to have poor support for compiling classes to target older versions of Java. It always supported the previous version, but often no more.
Even if you could compile for previous version, you had to be careful not to use functionality which did exist in the previous versions.
Java 7
Java 7 addresses both these issues. Firstly, it supports sources back to 1.2 and targets back to Java 1.1. Secondly. it insists you set the bootclasspath so you can include the version of the libraries you will be using for that version.
public class Main {
public static void main(String[] args) {
System.out.println("Hello World!");
}
}
$ javac -target 1.7 -source 1.7 Main.java
$ javac -target 1.6 -source 1.6 Main.java
warning: [options] bootstrap class path not set in conjunction with -source 1.6
1 warning
$ javac -Xbootclasspath:/usr/java/jdk1.6.0_29/jre/lib/rt.jar -target 1.6 -source 1.6 Main.java
$ javac -Xbootclasspath:/usr/java/jdk1.5.0_22/jre/lib/rt.jar -target 1.5 -source 1.5 Main.java
$ javac -Xbootclasspath:/usr/java/jdk1.4.0_30/jre/lib/rt.jar -target 1.4 -source 1.4 Main.java
$ javac -Xbootclasspath:/usr/java/jdk1.3.1_29/jre/lib/rt.jar -target 1.3 -source 1.3 Main.java
$ javac -Xbootclasspath:/usr/java/jdk1.2.2_017/jre/lib/rt.jar -target 1.2 -source 1.2 Main.java
$ javac -Xbootclasspath:/usr/java/jdk1.1.8_16/jre/lib/rt.jar -target 1.1 -source 1.2 Main.java
$ javac -Xbootclasspath:/usr/java/jdk1.1.8_16/jre/lib/rt.jar -target 1.1 -source 1.1 Main.java
javac: invalid source release: 1.1
Usage: javac
use -help for a list of possible options
$ javac -Xbootclasspath:/usr/java/jdk1.1.8_16/jre/lib/rt.jar -target 1.0 -source 1.0 Main.java
javac: invalid target release: 1.0
Usage: javac
use -help for a list of possible options
BTW: All the previous versions back to 1.1 are available from the Oracle web site Oracle Java Archive
Its pretty important to know -target and -source switch as there are times when you work in legacy application which is not running on Java5 and your IDE accidentally copied something available to Java5 only.
You still have to watch how many objects you create. This article looks at a benchmark passing events over TCP/IP at 4 billion events per minute using the net.openhft.chronicle.wire.channel package in Chronicle Wire and why we still avoid object allocations.. One of the key optimisations is creating almost no garbage. Allocation is a very cheap operation and collection of very short-lived objects is also very cheap. Does this really make a difference? What difference does one small object per event (44 bytes) make to the performance in a throughput test where GC pauses are amortised? While allocation is as efficient as possible, it doesn’t avoid the memory pressure on the L1/L2 caches of your CPUs and when many cores are busy, they are contending for memory in the shared L3 cache. Results Benchmark on a Ryzen 5950X with Ubuntu 22.10. JVM Vendor, Version No objects Throughput, Average Latency* One object per event Throughput, Average Latency* Azul Zulu 1.8.0_322 60.6 M event/s, 528
A Unique Identifier can be very useful for tracing. Those ids are even more useful when they contain a high-resolution timestamp. Not only do they record the time of an event, but if unique can help trace events as they pass through the system. Such unique timestamps however can be expensive depending on how they are implemented. This post explores a lightweight means of producing a unique, monotonically increasing system-wide nano-second resolution timestamp available in our open-source library. Uses for Unique Identifiers Unique identifiers can be useful to associate with a piece of information so that information can be referred to later unambiguously. This could be an event, a request, an order id, or a customer id. They can naturally be used as a primary key in a database or key/value store to retrieve that information later. One of the challenges of generating these identifiers is avoiding creating duplicates while not having an increasing cost. You could record every identi
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Its pretty important to know -target and -source switch as there are times when you work in legacy application which is not running on Java5 and your IDE accidentally copied something available to Java5 only.
ReplyDeleteThanks
What is the problem while using "==" in autoboxing world in Java 5 ?
i really need a clear explanation on how to set a class path as you mentioned
ReplyDeleteYou use the command line specified above, what is your doubt?
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