Java is an actively used programming language created in 1995. Java is a general-purpose computer programming language that is concurrent, class-based, object-oriented, and specifically designed to have as few implementation dependencies as possible. It is intended to let application developers "write once, run anywhere" (WORA), meaning that compiled Java code can run on all platforms that support Java without the need for recompilation. Java applications are typically compiled to bytecode that can run on any Java virtual machine (JVM) regardless of computer architecture. Read more on Wikipedia...

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Example code from the Hello World Collection:

// Hello World in Java

class HelloWorld {
  static public void main( String args[] ) {
    System.out.println( "Hello World!" );
  }
}

Example code from Linguist:

/**
 *   Copyright (c) Rich Hickey. All rights reserved.
 *   The use and distribution terms for this software are covered by the
 *   Eclipse Public License 1.0 (http://opensource.org/licenses/eclipse-1.0.php)
 *   which can be found in the file epl-v10.html at the root of this distribution.
 *   By using this software in any fashion, you are agreeing to be bound by
 * 	 the terms of this license.
 *   You must not remove this notice, or any other, from this software.
 **/

/* rich Apr 19, 2008 */

package clojure.lang;

import java.lang.ref.Reference;
import java.math.BigInteger;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;
import java.lang.ref.SoftReference;
import java.lang.ref.ReferenceQueue;

public class Util{
static public boolean equiv(Object k1, Object k2){
	if(k1 == k2)
		return true;
	if(k1 != null)
		{
		if(k1 instanceof Number && k2 instanceof Number)
			return Numbers.equal((Number)k1, (Number)k2);
		else if(k1 instanceof IPersistentCollection || k2 instanceof IPersistentCollection)
			return pcequiv(k1,k2);
		return k1.equals(k2);
		}
	return false;
}

static public boolean equiv(long k1, long k2){
	return k1 == k2;
}

static public boolean equiv(Object k1, long k2){
	return equiv(k1, (Object)k2);
}

static public boolean equiv(long k1, Object k2){
	return equiv((Object)k1, k2);
}

static public boolean equiv(double k1, double k2){
	return k1 == k2;
}

static public boolean equiv(Object k1, double k2){
	return equiv(k1, (Object)k2);
}

static public boolean equiv(double k1, Object k2){
	return equiv((Object)k1, k2);
}

static public boolean equiv(boolean k1, boolean k2){
	return k1 == k2;
}

static public boolean equiv(Object k1, boolean k2){
	return equiv(k1, (Object)k2);
}

static public boolean equiv(boolean k1, Object k2){
	return equiv((Object)k1, k2);
}

static public boolean equiv(char c1, char c2) {
    return c1 == c2;
}

static public boolean pcequiv(Object k1, Object k2){
	if(k1 instanceof IPersistentCollection)
		return ((IPersistentCollection)k1).equiv(k2);
	return ((IPersistentCollection)k2).equiv(k1);
}

static public boolean equals(Object k1, Object k2){
	if(k1 == k2)
		return true;
	return k1 != null && k1.equals(k2);
}

static public boolean identical(Object k1, Object k2){
	return k1 == k2;
}

static public Class classOf(Object x){
	if(x != null)
		return x.getClass();
	return null;
}

static public int compare(Object k1, Object k2){
	if(k1 == k2)
		return 0;
	if(k1 != null)
		{
		if(k2 == null)
			return 1;
		if(k1 instanceof Number)
			return Numbers.compare((Number) k1, (Number) k2);
		return ((Comparable) k1).compareTo(k2);
		}
	return -1;
}

static public int hash(Object o){
	if(o == null)
		return 0;
	return o.hashCode();
}

static public int hasheq(Object o){
	if(o == null)
		return 0;
	if(o instanceof Number)
		return Numbers.hasheq((Number)o);
	else if(o instanceof IHashEq)
		return ((IHashEq)o).hasheq();
	return o.hashCode();
}

static public int hashCombine(int seed, int hash){
	//a la boost
	seed ^= hash + 0x9e3779b9 + (seed << 6) + (seed >> 2);
	return seed;
}

static public boolean isPrimitive(Class c){
	return c != null && c.isPrimitive() && !(c == Void.TYPE);
}

static public boolean isInteger(Object x){
	return x instanceof Integer
			|| x instanceof Long
	        || x instanceof BigInt
			|| x instanceof BigInteger;
}

static public Object ret1(Object ret, Object nil){
		return ret;
}

static public ISeq ret1(ISeq ret, Object nil){
		return ret;
}

static public <K,V> void clearCache(ReferenceQueue rq, ConcurrentHashMap<K, Reference<V>> cache){
		//cleanup any dead entries
	if(rq.poll() != null)
		{
		while(rq.poll() != null)
			;
		for(Map.Entry<K, Reference<V>> e : cache.entrySet())
			{
            Reference<V> val = e.getValue();
			if(val != null && val.get() == null)
				cache.remove(e.getKey(), val);
			}
		}
}

static public RuntimeException runtimeException(String s){
	return new RuntimeException(s);
}

static public RuntimeException runtimeException(String s, Throwable e){
	return new RuntimeException(s, e);
}

/**
 * Throw even checked exceptions without being required
 * to declare them or catch them. Suggested idiom:
 * <p>
 * <code>throw sneakyThrow( some exception );</code>
 */
static public RuntimeException sneakyThrow(Throwable t) {
    // http://www.mail-archive.com/javaposse@googlegroups.com/msg05984.html
	if (t == null)
		throw new NullPointerException();
	Util.<RuntimeException>sneakyThrow0(t);
	return null;
}

@SuppressWarnings("unchecked")
static private <T extends Throwable> void sneakyThrow0(Throwable t) throws T {
	throw (T) t;
}

}

Example code from Wikipedia:

// Hello.java (Java SE 5)
import javax.swing.*;

public class Hello extends JFrame {
    public Hello() {
        super("hello");
        super.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
        super.add(new JLabel("Hello, world!"));
        super.pack();
        super.setVisible(true);
    }

    public static void main(final String[] args) {
        new Hello();
    }
}

Last updated July 8th, 2019