Master Google Guava: 40 Practical Examples to Supercharge Your Java Code

1. Guava Package Overview

Guava’s source packages cover a wide range of functionality. Key packages include:

com.google.common.base : core utilities such as Preconditions for argument validation and Optional for null‑safe handling.

com.google.common.collect : extended collection types like Multimap, Multiset, and many helper methods.

com.google.common.eventbus : a publish‑subscribe event bus for loosely coupled components.

com.google.common.hash : hashing utilities.

com.google.common.io : I/O helpers for file and stream operations.

com.google.common.math : arithmetic utilities for large numbers.

com.google.common.net : networking helpers such as URL handling.

com.google.common.primitives : static methods for primitive types.

com.google.common.reflect : reflection utilities.

com.google.common.util.concurrent : concurrency helpers including asynchronous computation and thread‑pool management.

2. String Handling Utilities

import com.google.common.base.CharMatcher;
import com.google.common.base.Joiner;
import com.google.common.base.Splitter;
import com.google.common.base.Strings;
import com.google.common.io.CharStreams;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.nio.charset.Charset;

public class GuavaDemo {
    public static void main(String[] args) throws IOException {
        // 1. Joiner concatenates a list with ", "
        String joined = Joiner.on(", ").join("apple", "banana", "cherry");
        System.out.println(joined); // apple, banana, cherry

        // 2. Splitter splits the string and trims results
        Iterable<String> parts = Splitter.on(",").trimResults().split(joined);
        for (String s : parts) {
            System.out.println(s); // each element on a new line
        }

        // 3. Strings utilities for null/empty handling
        String nullStr = null;
        String emptyStr = "";
        String wsStr = "   ";
        System.out.println(Strings.nullToEmpty(nullStr)); // prints empty string
        System.out.println(Strings.isNullOrEmpty(emptyStr)); // true
        System.out.println(Strings.isNullOrEmpty(wsStr)); // false
        System.out.println(CharMatcher.whitespace().removeFrom(wsStr)); // empty string

        // 4. Charset handling and reading a resource file
        Charset utf8 = Charsets.UTF_8;
        try (InputStream in = GuavaDemo.class.getResourceAsStream("/test.txt");
             InputStreamReader reader = new InputStreamReader(in, utf8)) {
            String content = CharStreams.toString(reader);
            System.out.println(content); // prints file content assuming UTF‑8
        }

        // 5. CaseFormat conversion
        String camel = "ExampleClassName";
        String lower = CaseFormat.UPPER_CAMEL.to(CaseFormat.LOWER_UNDERSCORE, camel);
        System.out.println(lower); // example_class_name
        String back = CaseFormat.LOWER_UNDERSCORE.to(CaseFormat.UPPER_CAMEL, lower);
        System.out.println(back); // ExampleClassName

        // 6. CharMatcher examples
        String input = "Hello, World! This is a test string.";
        String noVowels = CharMatcher.is('a','e','i','o','u').removeFrom(input);
        System.out.println(noVowels); // Hll, Wrld! Ths s tst strng.
        String replaceVowels = CharMatcher.is('a','e','i','o','u').replaceFrom(input, '*');
        System.out.println(replaceVowels); // H*ll*, W*rld! Th*s *s * t*st str*ng.
        String keepVowels = CharMatcher.is('a','e','i','o','u').retainFrom(input);
        System.out.println(keepVowels); // eiooeiae

        // 7. CharSequences utilities
        int idx = CharSequences.indexOf(input, "test");
        System.out.println("Index: " + idx); // 21
        boolean eq = CharSequences.equals("Hello", "Hello");
        System.out.println("Equal: " + eq); // true
        String concat = CharSequences.concat("Guava ", "is ", "awesome!").toString();
        System.out.println(concat); // Guava is awesome!
    }
}

3. Primitive Type Utilities

import com.google.common.primitives.Booleans;
import com.google.common.primitives.Bytes;
import com.google.common.primitives.Chars;
import com.google.common.primitives.Doubles;
import com.google.common.primitives.Floats;
import com.google.common.primitives.Ints;
import com.google.common.primitives.Longs;
import com.google.common.primitives.Shorts;
import java.util.Arrays;

public class GuavaPrimitivesExample {
    public static void main(String[] args) {
        int[] intArr = {1,2,3,4,5};
        int sumInts = Ints.sum(intArr);
        System.out.println("Sum of ints: " + sumInts); // 15

        long[] longArr = {1L,2L,3L,4L,5L};
        long sumLongs = Longs.sum(longArr);
        System.out.println("Sum of longs: " + sumLongs); // 15

        double[] dblArr = {1.1,2.2,3.3,4.4,5.5};
        double sumDoubles = Doubles.sum(dblArr);
        System.out.println("Sum of doubles: " + sumDoubles); // 16.5

        float[] fltArr = {1.1f,2.2f,3.3f,4.4f,5.5f};
        float sumFloats = Floats.sum(fltArr);
        System.out.println("Sum of floats: " + sumFloats); // 16.5

        boolean[] boolArr = {true,false,true};
        boolean anyTrue = Booleans.contains(boolArr, true);
        System.out.println("Array contains true: " + anyTrue); // true

        byte[] byteArr = {1,2,3,4,5};
        byte minByte = Bytes.min(byteArr);
        System.out.println("Min byte: " + minByte); // 1

        short[] shortArr = {1,2,3,4,5};
        short maxShort = Shorts.max(shortArr);
        System.out.println("Max short: " + maxShort); // 5

        char[] charArr = {'a','b','c','d','e'};
        int countC = Chars.count(charArr, 'c');
        System.out.println("Count of 'c': " + countC); // 1

        int[] unsorted = {5,3,1,4,2};
        Arrays.sort(unsorted);
        System.out.println("Sorted int array: " + Arrays.toString(unsorted)); // [1,2,3,4,5]
    }
}

4. I/O Helper Classes

import com.google.common.base.Charsets;
import com.google.common.base.Supplier;
import com.google.common.io.ByteStreams;
import com.google.common.io.CharStreams;
import com.google.common.io.InputSupplier;
import com.google.common.io.OutputSupplier;
import com.google.common.io.Resources;
import java.io.*;
import java.net.URL;

public class GuavaIoExample {
    public static void main(String[] args) throws IOException {
        // InputSupplier example
        InputSupplier<InputStream> inSup = new InputSupplier<InputStream>() {
            @Override public InputStream getInput() throws IOException {
                return new ByteArrayInputStream("Hello, Guava!".getBytes(Charsets.UTF_8));
            }
        };
        String fromInSup = new String(ByteStreams.toByteArray(inSup.getInput()), Charsets.UTF_8);
        System.out.println("From InputSupplier: " + fromInSup);

        // OutputSupplier example
        OutputSupplier<OutputStream> outSup = new OutputSupplier<OutputStream>() {
            @Override public OutputStream getOutput() throws IOException {
                return new ByteArrayOutputStream();
            }
        };
        OutputStream out = outSup.getOutput();
        out.write("Hello, from OutputSupplier!".getBytes(Charsets.UTF_8));
        ((ByteArrayOutputStream) out).close();

        // Resources example
        URL url = Resources.getResource("somefile.txt");
        String fromRes = Resources.toString(url, Charsets.UTF_8);
        System.out.println("From Resources: " + fromRes);

        // ByteStreams copy example
        InputStream src = new ByteArrayInputStream("Data to copy".getBytes(Charsets.UTF_8));
        ByteArrayOutputStream dst = new ByteArrayOutputStream();
        ByteStreams.copy(src, dst);
        String copied = new String(dst.toByteArray(), Charsets.UTF_8);
        System.out.println("Copied Data: " + copied);

        // CharStreams read example
        Reader reader = new StringReader("Characters to read");
        String fromChar = CharStreams.toString(reader);
        System.out.println("From CharStreams: " + fromChar);

        // try‑with‑resources for safe closing
        try (StringWriter sw = new StringWriter()) {
            sw.write("Hello, try-with-resources!");
            String written = sw.toString();
            System.out.println("Written Data: " + written);
        }
    }
}

5. Miscellaneous Utilities

import com.google.common.base.Charsets;
import com.google.common.base.Throwables;
import com.google.common.hash.HashCode;
import com.google.common.hash.Hashing;
import com.google.common.io.BaseEncoding;
import com.google.common.io.ClassPath;
import com.google.common.util.concurrent.Uninterruptibles;
import java.io.IOException;
import java.io.InputStream;
import java.net.URL;
import java.util.concurrent.TimeUnit;

public class GuavaUtilitiesExample {
    public static void main(String[] args) {
        // Stopwatch timing
        Stopwatch sw = Stopwatch.createStarted();
        Uninterruptibles.sleepUninterruptibly(1, TimeUnit.SECONDS);
        long elapsed = sw.elapsed(TimeUnit.MILLISECONDS);
        System.out.println("Elapsed time: " + elapsed + " ms");

        // ClassPath scanning (caution: may be heavy)
        try {
            ClassPath cp = ClassPath.from(GuavaUtilitiesExample.class.getClassLoader());
            for (ClassPath.ClassInfo ci : cp.getAllClasses()) {
                if (ci.getName().contains("Guava")) {
                    System.out.println("Class found: " + ci.getName());
                }
            }
        } catch (IOException e) {
            Throwables.throwIfUnchecked(e);
        }

        // BaseEncoding (Base64) example
        String txt = "Hello, Guava!";
        String encoded = BaseEncoding.base64().encode(txt.getBytes(Charsets.UTF_8));
        byte[] decodedBytes = BaseEncoding.base64().decode(encoded);
        String decoded = new String(decodedBytes, Charsets.UTF_8);
        System.out.println("Original text: " + txt);
        System.out.println("Encoded text: " + encoded);
        System.out.println("Decoded text: " + decoded);

        // Throwables root cause example
        try {
            throw new RuntimeException("Outer exception", new IOException("Inner exception"));
        } catch (Exception e) {
            Throwable root = Throwables.getRootCause(e);
            System.out.println("Root cause: " + root.getMessage());
        }

        // HashCode (SHA‑256) example
        String toHash = "This is some text to hash";
        HashCode hc = Hashing.sha256().hashString(toHash, Charsets.UTF_8);
        System.out.println("SHA-256 hash: " + hc);
    }
}

ClassPath scans all classes on the class loader; use cautiously to avoid performance impact.

BaseEncoding provides convenient Base64 encoding/decoding.

Throwables helps retrieve the root cause of nested exceptions.

HashCode represents hash values (e.g., SHA‑256) distinct from Objects.hash().