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I know I know, not another tips question. But I'm rather surprised that this question hasn't already been posted. At any rate, are there any useful shortcuts that can be used especially in Java?

As shown below, import already adds at least 17 characters to a program.

import java.io.*;

I understand that the simple solution would be to use another language, but it seems to be a real challenge to shorten Java programs.

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3  
package can be skipped. –  st0le Jul 19 '12 at 7:08
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14 Answers

  • Use the most recent possible java. Java 8 lets you use lambda expressions, so use it if you need anything even like functional objects.

  • Define shortened functions for things you use a lot. For instance, you have a hundred calls to exampleClassInstance.doSomething(someParameter), define a new function void d(ParameterType p){exampleClassInstance.doSomething(p)} and use it to save yourself some characters.

  • If you are using a particular long class name more than once, like

    MyEventHandlerProxyQueueExecutorServiceCollectionAccessManagerFactory
    

    instead define a new class:

    class X extends MyEventHandlerProxyQueueExecutorServiceCollectionAccessManagerFactory{}
    

    If you are only using one particular method of that class (but still need to instantiate it), you can define a shortened version inside the new class at the same time.

  • Use function type parameters to shorten things, where possible, like this:

    <T>void p(T o){System.out.println(o);}
    
  • Use for(;;) instead of while(true).

  • Do not use access modifiers unless absolutely necessary.

  • Do not use final for anything.

  • Never put a block after a for loop. Additional statements should be placed inside the for statement itself, like for(int i=0;i<m;a(i),b(++i))c(i);.

  • Use inline assignment, incrementation, instantiation. Use anonymous inline classes where appropriate. Use lambdas instead if possible. Nest function calls. Some functions are guaranteed to return their parent object, these ones are actually even meant to be chained together.

  • Your main method throws Exceptions, not catches them.

  • Error is shorter than Exception. If for some reason you really need to throw messages up the stack, use an Error, even if it is perfectly normal situation.

  • If some condition would require immediate termination, use int a=1/0; rather than throw null; or System.exit(0);. At run time, this throws an ArithmeticException. If you already have a numeric variable in your code, use it instead. (If you already have import static java.lang.System.*;, go with exit(0);.)

  • Instead of implementing interfaces, like List<E>, extend an immediate (or not-so-immediate, if there is any advantage to doing so at all) child class, like AbstractList<E>, which provides default implementations of most of the methods, and requires only the implementation of a few key pieces.

  • Write your code out in longhand first, with newlines, indentation, and full variable names. Once you have working code, then you can shorten names, move declarations around, and add shortcut methods. By writing it out long to start, you give yourself more opportunity to simplify the program as a whole.

  • Compare alternative optimizations to a piece of code, because the most optimal strategy can change dramatically with very small changes to the code. For instance:

    • If you have only up to two calls to Arrays.sort(a), the most efficient way to is to call it with its fully qualified name, java.util.Arrays.sort(a).
    • With three or more calls, it is more efficient to instead add a shortcut method void s(int[]a){java.util.Arrays.sort(a);}. This should still use the fully-qualified name in this case. (If you need more than one overload, you are probably doing it wrong.)
    • However, if your code needs to also copy an array at some point (usually done with a short for loop in golfing, in the absence of an easily-accessible library method), you can take advantage of Arrays.copyOf to do the task. When more than one method is used, and there are 3 or more calls, doing import static java.util.Arrays.*; is the most efficient way of referring to those methods. After that, only if you have more than 8 separate calls to sort should you be using a shortcut method for it, and only at 5 or more calls is a shortcut warranted for copyOf.

    The only real way of performing such analysis on code is to actually perform potential modifications on copies of the code, and then compare the results.

  • Avoid using someTypeValue.toString(); method, instead just append someTypeValue+"".

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With a static import:

import static java.lang.System.out;
// even shorter (thanks to Johannes Kuhn):
import static java.lang.System.*;

you can save some boilerplate later, but you need multiple invocations to reach a payoff:

public static void main (String[] args) {
    out.println ("foo");    
    out.println ("bar");    
    out.println ("baz");    
}
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3  
:O. You can do this?! And all this time I thought that this was impossible in Java! –  Quincunx Dec 20 '13 at 7:17
4  
you can even use import static java.lang.System.*. –  Johannes Kuhn Dec 20 '13 at 19:16
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Rather than using the import static java.lang.System.* technique to save on println() statements, I've found that defining the following method is much more effective at saving characters:

static<T>void p(T p){
    System.out.println(p);
}

This is because it can be invoked as p(myString) rather than out.println(myString) which has a much quicker and more dramatic character payoff.

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The argument to main doesn't have to be called args, and you can cut some whitespace:

public static void main(String[]a){}

will do just fine.

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I don't know if you would consider this 'pure' Java, but Processing allows you to create programs with little initial setup (completed automatically).

For console output, you can have something as simple as:

println("hi"); //done

for graphical output, a little more:

void setup() {
  size(640,480);
}
void draw() {
  fill(255,0,0); //color used to fill shapes
  rect(50,50,25,25); //25x25 pixel square at x=50,y=50
}
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+1 Excellent resource! I'll be sure to play around with it. –  mdeitrick Jul 19 '12 at 19:07
    
Would it be alright if I added other people's answers to this one? Or does that defeat the purpose of a community wiki? –  mdeitrick Sep 16 '12 at 13:45
1  
By the way, you do not even have to call size at all; it will default to a 100 by 100 pixel square. In most OSes, the frame around it will be about twice that large, with the square centered and the rest of the area filled with content taken from the desktop. –  AJMansfield Dec 20 '13 at 12:32
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For golfing that doesn't require input, you can use static blocks, and run it just fine without any main method, just compile it with Java 6.

public class StaticExample{
    static {
        //do stuff
    }
}
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1  
Did you try to compile and run it? This block is run when the class gets loaded by the class loader. But the class loader won't load anything until it knows of a class with a main method. –  Cruncher Dec 20 '13 at 15:31
    
@Cruncher You can get around that by yourself telling java on the command line/in a manifest file which class to load. –  AJMansfield Dec 22 '13 at 1:20
    
@AJMansfield I'm pretty sure the manifest file is to tell java which class has main. If it doesn't have main in it, it shouldn't load it –  Cruncher Dec 23 '13 at 23:49
3  
@Cruncher, this worked with Java 6. Java 7 changed the way it works. –  Peter Taylor Dec 31 '13 at 18:36
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If you are going to be using some method a lot, assign its resident class to a variable. For example, assign System.out to a variable:

java.io.PrintStream o=System.out;
//now I can call o.print() or o.println() to the same effect as System.out.println()

Also for Integer.parseInt():

Integer i=1;
i.parseInt("some string");

This will almost surely trigger an ide warning about "accessing static method from variable"

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If you use enum instead of class, you save one character.

enum NoClass {
    F, G, H;    
    public static void main (String[] args) {

    }
}

But you have to introduce at least one enum instance (F, G, H in this example) which have to payoff themselves.

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Seems you don't need any enum instances. I did enum M{;public static void main(String[]a){...} with no problems. –  Danny Jan 27 at 14:47
    
@Danny But then it doesn't save any characters. class M{ is exactly the same length as enum M{;. In that case, I'd go with the class because it is prettier (IMO) –  Quincunx Feb 21 at 23:32
    
at least for me enum{ worked without a ; after; its only the IDE moaning that there is a error butthe compiler accepts it –  masterX244 Mar 5 at 22:30
    
@masterX244 What compiler/version? Mine throws a tantrum and won't do it. –  Geobits Apr 16 at 14:04
    
worked on java 1.7 for me (appeared s, ned to investigate further cause with a update to .8 it stopped working) –  masterX244 Apr 16 at 17:41
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If you ever have to use the boolean expressions true or false, replace them with 1>0 and 1<0 respectively.

For example:

boolean found=false;
for(i=0; i<10; i++) if(a[i]==42) found=true;

This linear search example can be reduced to

boolean f=1<0;
for(i=0;i<10;)if(a[i++]==42)f=1>0;
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3  
If you're going to need a lot of true/false, just add boolean t=1>0,f=1<0;. Then instead of 1>0, use t and save two chars per use. Payoff over 1>0 method comes at 10 uses. –  Geobits Mar 11 at 2:17
    
Remember kids, 1==True and 0==False. Implicit conversion is also allowed. –  Synthetica Apr 9 at 17:48
    
@Synthetica Not in Java. ideone.com/kSRTTZ –  ace Apr 9 at 17:55
    
@ace Isn't it? Huh, my memory has failed me then. –  Synthetica Apr 9 at 17:56
4  
@Geobits: boolean t=1>0,f=!t; - one char shorter! –  bobbel Apr 11 at 14:07
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If you need to grab a number from an argument (or any other string), normally you see something like:

public static void main(String[]a){
    int n=Integer.valueOf(a[0]);
    ...
}

Many times, you don't need an Integer. Plenty of challenges don't use large numbers. Since Short and Byte will both unbox to an int, use the more appropriate valueOf() instead and save a couple bytes.

Keep your actual variable as an int, though, since it's shorter than both byte and short:

int n=Byte.valueOf(a[0]);

If you need to do this for multiple numbers, you can combine with this method:

Byte b=1;
int n=b.valueOf(a[0]),m=b.valueOf(a[1])...
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We all know about the bitwise xor (^), but it is also a logical xor. In fact, it is the only boolean logic binary operator that uses only 1 char.

So (a||b)&&!(a&&b) simply becomes a^b.

Probably the biggest use of this, other than obvious simplifications such as above, is to replace || when the conditions are mutually exclusive. However, remember that the bitwise ^ has higher precedence.

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As long as you remember precedence, you can use & and | also. It might be useful if your conditions are already in parentheses, or if you're already working with booleans. –  Geobits Apr 16 at 18:23
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Don't use Random!

In general, if you need random numbers, Random is a horrible way to go about it*. Much better to use Math.random() instead. To use Random, you need to do this (let's say we need an int):

import java.util.*;
Random r=new Random();
a=r.nextInt(9);
b=r.nextInt(9);

Compare that to:

a=(int)(Math.random()*9);
b=(int)(Math.random()*9);

and:

int r(int m){return(int)(Math.random()*m);}
a=r(9);
b=r(9);

The first method takes 41+15n characters (n is number of calls). The second is 25n characters, and the third is 43+7n.

So, if you only need it once or twice, use the inline Math.random() method. For three or more calls, you'll save by using a function. Either one saves characters on the first use over Random.


If you're already using Math.random() for double, remember that at four uses, it's still a savings to pull it out into:

double r(){return Math.random();}

For 33 characters, you'll save 10 on each call to r()

* Unless you have to seed the PRNG for predictable results. Then, I don't see much of a way around it.

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1  
Don't forget about Random#nextGaussian though. –  Quincunx yesterday
    
@Quincunx True, doing the math to get a good normal distribution would lose you any savings you got. I'll just refer to that as the exception that proves the rule ;) –  Geobits yesterday
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another trick i used once was when i needed a Array varialbe inside a function and the parameter of it had the sam e type. abused the vararg way for that (best used when a called function returns a array like

T doSomethingWithString(String... x)
{
    x=x[0].split("someregex");
    //some code using the elements
    return something;
}
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Using Java Applet can save you a lot of space:

import java.applet.Applet;

public class B extends Applet{
    public B(){
        System.out.print("Hello world!");
    }
}

Output:

Hello world!

Also this can be even more shorten by making be to extends nothing.

public class B{
    public B(){
        System.out.print("Hello world!");
    }
}

How ever in additional to desired output we will also get exception:

Output:

Hello world!
java.lang.ClassCastException: B cannot be cast to java.applet.Applet
at sun.applet.AppletPanel.createApplet(Unknown Source)
at sun.applet.AppletPanel.runLoader(Unknown Source)
at sun.applet.AppletPanel.run(Unknown Source)
at java.lang.Thread.run(Unknown Source)

Also you can combine this with static block and save another 4 bytes like this:

public class B{
    static{
        System.out.println("Hello world!");
    }
}

Same output with exception as above.

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