Guava Idioms

README.md

This gist is a small demonstration of using Guava's Preconditions class to more concisely express preconditions and assertions. Often, methods and constructors have stanzas such as the following declared:

public static boolean doSomething(final Object param1, final Object param2) {

    if (param1 == null) {
        throw InvalidArgumentException("doSomething requires a non-null value for param1");
    }
    
    if (param2 == null) {
        throw InvalidArgumentException("doSomething requires a non-null value for param2");
    }
    
    // do work ...
    
}

The checkArgument and checkState methods shorten these checks.

N.B. This could be further simplified by introducing two additional utility methods wrapping checkArgument -- checkArgumentNotNull and checkArgumentNotBlank.

Files.java

package net.cockamamy.playpen.utils;

import static java.lang.String.format;

import static com.google.common.base.Preconditions.checkArgument;
import static com.google.common.base.Preconditions.checkState;

public final class Files {
    
    public static File openFile(final File aParentDirectory, final String aFileName) {

        checkArgument(aParentDirectory != null, format(
                "%1$s.createFile requires a non-null parent directory.",
                FileUtilities.class.getName()));
        checkArgument(isNotBlank(aFileName) : format(
                "%1$s.createFile requires a non-blank file name.",
                FileUtilities.class.getName()));

        final File aFile = new File(aParentDirectory, aFileName);
        checkState(!aFile.exists(), format(
                    "%1$s does not contain %2$s", aParentDirectory.getName(),
                    aFileName)));
        
        return aFile;
        
    }
    
}