Guava - Quick Guide

Guava - Overview

What is Guava?

Guava is an open source, Java-based library and contains many core libraries of Google, which are being used in many of their projects. It facilitates best coding practices and helps reduce coding errors. It provides utility methods for collections, caching, primitives support, concurrency, common annotations, string processing, I/O, and validations.

Benefits of Guava

• Standardized − The Guava library is managed by Google.

• Efficient − It is a reliable, fast, and efficient extension to the Java standard library.

• Optimized − The library is highly optimized.

• Functional Programming − It adds functional processing capability to Java.

• Utilities − It provides many utility classes which are regularly required in programming application development.

• Validation − It provides a standard failsafe validation mechanism.

• Best Practices − It emphasizes on best practices.

Consider the following code snippet.

public class GuavaTester {
   public static void main(String args[]) {
      GuavaTester guavaTester = new GuavaTester();
      
      Integer a =  null;
      Integer b =  new Integer(10);
      System.out.println(guavaTester.sum(a,b));
   }

   public Integer sum(Integer a, Integer b) {
      return a + b;
   }	
}

Run the program to get the following result.

Exception in thread "main" java.lang.NullPointerException
   at GuavaTester.sum(GuavaTester.java:13)
   at GuavaTester.main(GuavaTester.java:9)

Following are the problems with the code.

• sum() is not taking care of any of the parameters to be passed as null.

• caller function is also not worried about passing a null to the sum() method accidently.

• When the program runs, NullPointerException occurs.

In order to avoid the above problems, null check is to be made in each and every place where such problems are present.

Let's see the use of Optional, a Guava provided Utility class, to solve the above problems in a standardized way.

import com.google.common.base.Optional;

public class GuavaTester {
   public static void main(String args[]) {
      GuavaTester guavaTester = new GuavaTester();

      Integer invalidInput = null;
      Optional<Integer> a =  Optional.of(invalidInput);
      Optional<Integer> b =  Optional.of(new Integer(10));
      System.out.println(guavaTester.sum(a,b));      
   }

   public Integer sum(Optional<Integer> a, Optional<Integer> b) {
      return a.get() + b.get();
   }	
}

Run the program to get the following result.

Exception in thread "main" java.lang.NullPointerException
	at com.google.common.base.Preconditions.checkNotNull(Preconditions.java:210)
	at com.google.common.base.Optional.of(Optional.java:85)
	at GuavaTester.main(GuavaTester.java:8)

Let's understand the important concepts of the above program.

• Optional − A utility class, to make the code use the null properly.

• Optional.of − It returns the instance of Optional class to be used as a parameter. It checks the value passed, not to be ‘null’.

• Optional.get − It gets the value of the input stored in the Optional class.

Using the Optional class, you can check whether the caller method is passing a proper parameter or not.

Guava - Environment Setup

Local Environment Setup

If you are still willing to set up your environment for Java programming language, then this section guides you on how to download and set up Java on your machine. Please follow the steps mentioned below to set up the environment.

Java SE is freely available from the link Download Java. So you download a version based on your operating system.

Follow the instructions to download Java and run the .exe to install Java on your machine. Once you have installed Java on your machine, you would need to set environment variables to point to correct installation directories −

Setting up the Path for Windows 2000/XP

We are assuming that you have installed Java in c:\Program Files\java\jdk directory −

• Right-click on 'My Computer' and select 'Properties'.

• Click on the 'Environment variables' button under the 'Advanced' tab.

• Now, alter the 'Path' variable so that it also contains the path to the Java executable. Example, if the path is currently set to 'C:\WINDOWS\SYSTEM32', then change your path to read 'C:\WINDOWS\SYSTEM32;c:\Program Files\java\jdk\bin'.

Setting up the Path for Windows 95/98/ME

We are assuming that you have installed Java in c:\Program Files\java\jdk directory −

• Edit the 'C:\autoexec.bat' file and add the following line at the end − 'SET PATH=%PATH%;C:\Program Files\java\jdk\bin'

Setting up the Path for Linux, UNIX, Solaris, FreeBSD

Environment variable PATH should be set to point to where the Java binaries have been installed. Refer to your shell documentation if you have trouble doing this.

Example, if you use bash as your shell, then you would add the following line to the end of your '.bashrc: export PATH=/path/to/java:$PATH'

Popular Java Editors

To write your Java programs, you need a text editor. There are many sophisticated IDEs available in the market. But for now, you can consider one of the following −

• Notepad − On Windows machine you can use any simple text editor like Notepad (Recommended for this tutorial), TextPad.

• Netbeans − It is a Java IDE that is open-source and free which can be downloaded from https://www.netbeans.org/index.html.

• Eclipse − It is also a Java IDE developed by the eclipse open-source community and can be downloaded from https://www.eclipse.org/.

Download Guava Archive

Download the latest version of Guava jar file from guava-18.0.jar. At the time of writing this tutorial, we have downloaded guava-18.0.jar and copied it into C:\>Guava folder.

Set Guava Environment

Set the Guava_HOME environment variable to point to the base directory location where Guava jar is stored on your machine. Assuming, we've extracted guava-18.0.jar in Guava folder on various Operating Systems as follows.

Set CLASSPATH Variable

Set the CLASSPATH environment variable to point to the Guava jar location. Assuming, you have stored guava-18.0.jar in Guava folder on various Operating Systems as follows.

Guava - Optional Class

Optional is an immutable object used to contain a not-null object. Optional object is used to represent null with absent value. This class has various utility methods to facilitate the code to handle values as available or not available instead of checking null values.

Class Declaration

Following is the declaration for com.google.common.base.Optional<T> class −

@GwtCompatible(serializable = true)
public abstract class Optional<T>
   extends Object
      implements Serializable

Class Methods

Methods Inherited

This class inherits methods from the following class −

• java.lang.Object

Example of Optional Class

Create the following java program using any editor of your choice in say C:/> Guava.

GuavaTester.java

import com.google.common.base.Optional;

public class GuavaTester {
   public static void main(String args[]) {
      GuavaTester guavaTester = new GuavaTester();

      Integer value1 =  null;
      Integer value2 =  new Integer(10);
      
      //Optional.fromNullable - allows passed parameter to be null.
      Optional<Integer> a = Optional.fromNullable(value1);
      
      //Optional.of - throws NullPointerException if passed parameter is null
      Optional<Integer> b = Optional.of(value2);		

      System.out.println(guavaTester.sum(a,b));
   }

   public Integer sum(Optional<Integer> a, Optional<Integer> b) {
      //Optional.isPresent - checks the value is present or not
      System.out.println("First parameter is present: " + a.isPresent());

      System.out.println("Second parameter is present: " + b.isPresent());

      //Optional.or - returns the value if present otherwise returns
      //the default value passed.
      Integer value1 = a.or(new Integer(0));	

      //Optional.get - gets the value, value should be present
      Integer value2 = b.get();

      return value1 + value2;
   }	
}

Verify the Result

Compile the class using javac compiler as follows −

C:\Guava>javac GuavaTester.java

Now run the GuavaTester to see the result.

C:\Guava>java GuavaTester

See the result.

First parameter is present: false
Second parameter is present: true
10

Guava - Preconditions Class

Preconditions provide static methods to check that a method or a constructor is invoked with proper parameter or not. It checks the pre-conditions. Its methods throw IllegalArgumentException on failure.

Class Declaration

Following is the declaration for com.google.common.base.Preconditions class −

@GwtCompatible
public final class Preconditions
   extends Object

Class Methods

Methods Inherited

This class inherits methods from the following class −

• java.lang.Object

Example of Preconditions Class

Create the following java program using any editor of your choice in say C:/> Guava.

GuavaTester.java

import com.google.common.base.Preconditions;

public class GuavaTester {

   public static void main(String args[]) {
      GuavaTester guavaTester = new GuavaTester();

      try {
         System.out.println(guavaTester.sqrt(-3.0));
      } catch(IllegalArgumentException e) {
         System.out.println(e.getMessage());
      }

      try {
         System.out.println(guavaTester.sum(null,3));
      } catch(NullPointerException e) {
         System.out.println(e.getMessage());
      }

      try {
         System.out.println(guavaTester.getValue(6));
      } catch(IndexOutOfBoundsException e) {
         System.out.println(e.getMessage());
      }
   }

   public double sqrt(double input) throws IllegalArgumentException {
      Preconditions.checkArgument(input > 0.0,
         "Illegal Argument passed: Negative value %s.", input);
      return Math.sqrt(input);
   }

   public int sum(Integer a, Integer b) {
      a = Preconditions.checkNotNull(a, "Illegal Argument passed: First parameter is Null.");
      b = Preconditions.checkNotNull(b, "Illegal Argument passed: Second parameter is Null.");

      return a+b;
   }

   public int getValue(int input) {
      int[] data = {1,2,3,4,5};
      Preconditions.checkElementIndex(input,data.length, "Illegal Argument passed: Invalid index.");
      return 0;
   }
}

Verify the Result

Compile the class using javac compiler as follows −

C:\Guava>javac GuavaTester.java

Now run the GuavaTester to see the result.

C:\Guava>java GuavaTester

See the result.

Illegal Argument passed: Negative value -3.0.
Illegal Argument passed: First parameter is Null.
Illegal Argument passed: Invalid index. (6) must be less than size (5)

Guava - Ordering Class

Ordering can be seen as an enriched comparator with enhanced chaining functionality, multiple utility methods, multi-type sorting capability, etc.

Class Declaration

Following is the declaration for com.google.common.collect.Ordering<T> class −

@GwtCompatible
public abstract class Ordering<T>
   extends Object
      implements Comparator<T>

Class Methods

Methods Inherited

This class inherits methods from the following class −

• java.lang.Object

Example of Ordering Class

Create the following java program using any editor of your choice in say C:/> Guava.

GuavaTester.java

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;

import com.google.common.collect.Ordering;

public class GuavaTester {
   public static void main(String args[]) {
      List<Integer> numbers = new ArrayList<Integer>();
      
      numbers.add(new Integer(5));
      numbers.add(new Integer(2));
      numbers.add(new Integer(15));
      numbers.add(new Integer(51));
      numbers.add(new Integer(53));
      numbers.add(new Integer(35));
      numbers.add(new Integer(45));
      numbers.add(new Integer(32));
      numbers.add(new Integer(43));
      numbers.add(new Integer(16));

      Ordering ordering = Ordering.natural();
      System.out.println("Input List: ");
      System.out.println(numbers);		
         
      Collections.sort(numbers,ordering );
      System.out.println("Sorted List: ");
      System.out.println(numbers);
         
      System.out.println("======================");
      System.out.println("List is sorted: " + ordering.isOrdered(numbers));
      System.out.println("Minimum: " + ordering.min(numbers));
      System.out.println("Maximum: " + ordering.max(numbers));
         
      Collections.sort(numbers,ordering.reverse());
      System.out.println("Reverse: " + numbers);

      numbers.add(null);
      System.out.println("Null added to Sorted List: ");
      System.out.println(numbers);		

      Collections.sort(numbers,ordering.nullsFirst());
      System.out.println("Null first Sorted List: ");
      System.out.println(numbers);
      System.out.println("======================");

      List<String> names = new ArrayList<String>();
      
      names.add("Ram");
      names.add("Shyam");
      names.add("Mohan");
      names.add("Sohan");
      names.add("Ramesh");
      names.add("Suresh");
      names.add("Naresh");
      names.add("Mahesh");
      names.add(null);
      names.add("Vikas");
      names.add("Deepak");

      System.out.println("Another List: ");
      System.out.println(names);

      Collections.sort(names,ordering.nullsFirst().reverse());
      System.out.println("Null first then reverse sorted list: ");
      System.out.println(names);
   }
}

Verify the Result

Compile the class using javac compiler as follows −

C:\Guava>javac GuavaTester.java

Now run the GuavaTester to see the result.

C:\Guava>java GuavaTester

See the result.

Input List: 
[5, 2, 15, 51, 53, 35, 45, 32, 43, 16]
Sorted List: 
[2, 5, 15, 16, 32, 35, 43, 45, 51, 53]
======================
List is sorted: true
Minimum: 2
Maximum: 53
Reverse: [53, 51, 45, 43, 35, 32, 16, 15, 5, 2]
Null added to Sorted List: 
[53, 51, 45, 43, 35, 32, 16, 15, 5, 2, null]
Null first Sorted List: 
[null, 2, 5, 15, 16, 32, 35, 43, 45, 51, 53]
======================
Another List: 
[Ram, Shyam, Mohan, Sohan, Ramesh, Suresh, Naresh, Mahesh, null, Vikas, Deepak]
Null first then reverse sorted list: 
[Vikas, Suresh, Sohan, Shyam, Ramesh, Ram, Naresh, Mohan, Mahesh, Deepak, null]

Guava - Objects Class

Objects class provides helper functions applicable to all objects such as equals, hashCode, etc.

Class Declaration

Following is the declaration for com.google.common.base.Objects class −

@GwtCompatible
public final class Objects
   extends Object

Class Methods

Methods Inherited

This class inherits methods from the following class −

• java.lang.Object

Example of Objects Class

Create the following java program using any editor of your choice in say C:/> Guava.

GuavaTester.java

import com.google.common.base.Objects;

public class GuavaTester {
   public static void main(String args[]) {
      Student s1 = new Student("Mahesh", "Parashar", 1, "VI");	
      Student s2 = new Student("Suresh", null, 3, null);	
	  
      System.out.println(s1.equals(s2));
      System.out.println(s1.hashCode());	
      System.out.println(
         Objects.toStringHelper(s1)
         .add("Name",s1.getFirstName()+" " + s1.getLastName())
         .add("Class", s1.getClassName())
         .add("Roll No", s1.getRollNo())
         .toString());
   }
}

class Student {
   private String firstName;
   private String lastName;
   private int rollNo;
   private String className;

   public Student(String firstName, String lastName, int rollNo, String className) {
      this.firstName = firstName;
      this.lastName = lastName;
      this.rollNo = rollNo;
      this.className = className;		
   }

   @Override
   public boolean equals(Object object) {
      if(!(object instanceof Student) || object == null) {
         return false;
      }
      Student student = (Student)object;
      // no need to handle null here		
      // Objects.equal("test", "test") == true
      // Objects.equal("test", null) == false
      // Objects.equal(null, "test") == false
      // Objects.equal(null, null) == true		
      return Objects.equal(firstName, student.firstName)  // first name can be null
         && Objects.equal(lastName, student.lastName)     // last name can be null
         && Objects.equal(rollNo, student.rollNo)	
         && Objects.equal(className, student.className);  // class name can be null
   }

   @Override
   public int hashCode() {
      //no need to compute hashCode by self
      return Objects.hashCode(className,rollNo);
   }
   
   public String getFirstName() {
      return firstName;
   }
   
   public void setFirstName(String firstName) {
      this.firstName = firstName;
   }
   
   public String getLastName() {
      return lastName;
   }
   
   public void setLastName(String lastName) {
      this.lastName = lastName;
   }
   
   public int getRollNo() {
      return rollNo;
   }
   
   public void setRollNo(int rollNo) {
      this.rollNo = rollNo;
   }
   
   public String getClassName() {
      return className;
   }
   
   public void setClassName(String className) {
      this.className = className;
   }
}

Verify the Result

Compile the class using javac compiler as follows −

C:\Guava>javac GuavaTester.java

Now run the GuavaTester to see the result.

C:\Guava>java GuavaTester

See the result.

false
85871
Student{Name=Mahesh Parashar, Class=VI, Roll No=1}

Guava - Range Class

Range represents an interval or a sequence. It is used to get a set of numbers/ strings lying in a particular range.

Class Declaration

Following is the declaration for com.google.common.collect.Range<C> class −

@GwtCompatible
public final class Range<C extends Comparable>
   extends Object
      implements Predicate<C>, Serializable

Methods

Methods Inherited

This class inherits methods from the following class −

• java.lang.Object

Example of Range Class

Create the following java program using any editor of your choice in say C:/> Guava.

GuavaTester.java

import com.google.common.collect.ContiguousSet;
import com.google.common.collect.DiscreteDomain;
import com.google.common.collect.Range;
import com.google.common.primitives.Ints;

public class GuavaTester {

   public static void main(String args[]) {
      GuavaTester tester = new GuavaTester();
      tester.testRange();
   }

   private void testRange() {

      //create a range [a,b] = { x | a <= x <= b}
      Range<Integer> range1 = Range.closed(0, 9);	
      System.out.print("[0,9] : ");
      printRange(range1);		
      
      System.out.println("5 is present: " + range1.contains(5));
      System.out.println("(1,2,3) is present: " + range1.containsAll(Ints.asList(1, 2, 3)));
      System.out.println("Lower Bound: " + range1.lowerEndpoint());
      System.out.println("Upper Bound: " + range1.upperEndpoint());

      //create a range (a,b) = { x | a < x < b}
      Range<Integer> range2 = Range.open(0, 9);
      System.out.print("(0,9) : ");
      printRange(range2);

      //create a range (a,b] = { x | a < x <= b}
      Range<Integer> range3 = Range.openClosed(0, 9);
      System.out.print("(0,9] : ");
      printRange(range3);

      //create a range [a,b) = { x | a <= x < b}
      Range<Integer> range4 = Range.closedOpen(0, 9);
      System.out.print("[0,9) : ");
      printRange(range4);

      //create an open ended range (9, infinity
      Range<Integer> range5 = Range.greaterThan(9);
      System.out.println("(9,infinity) : ");
      System.out.println("Lower Bound: " + range5.lowerEndpoint());
      System.out.println("Upper Bound present: " + range5.hasUpperBound());

      Range<Integer> range6 = Range.closed(3, 5);	
      printRange(range6);

      //check a subrange [3,5] in [0,9]
      System.out.println("[0,9] encloses [3,5]:" + range1.encloses(range6));

      Range<Integer> range7 = Range.closed(9, 20);	
      printRange(range7);
      
      //check ranges to be connected		
      System.out.println("[0,9] is connected [9,20]:" + range1.isConnected(range7));
      Range<Integer> range8 = Range.closed(5, 15);	

      //intersection
      printRange(range1.intersection(range8));

      //span
      printRange(range1.span(range8));
   }

   private void printRange(Range<Integer> range) {		
   
      System.out.print("[ ");
      
      for(int grade : ContiguousSet.create(range, DiscreteDomain.integers())) {
         System.out.print(grade +" ");
      }
      System.out.println("]");
   }
}

Verify the Result

Compile the class using javac compiler as follows −

C:\Guava>javac GuavaTester.java

Now run the GuavaTester to see the result.

C:\Guava>java GuavaTester

See the result.

[0,9] : [ 0 1 2 3 4 5 6 7 8 9 ]
5 is present: true
(1,2,3) is present: true
Lower Bound: 0
Upper Bound: 9
(0,9) : [ 1 2 3 4 5 6 7 8 ]
(0,9] : [ 1 2 3 4 5 6 7 8 9 ]
[0,9) : [ 0 1 2 3 4 5 6 7 8 ]
(9,infinity) : 
Lower Bound: 9
Upper Bound present: false
[ 3 4 5 ]
[0,9] encloses [3,5]:true
[ 9 10 11 12 13 14 15 16 17 18 19 20 ]
[0,9] is connected [9,20]:true
[ 5 6 7 8 9 ]
[ 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 ]

Guava - Throwables Class

Throwables class provides utility methods related to Throwable interface.

Class Declaration

Following is the declaration for com.google.common.base.Throwables class −

public final class Throwables
   extends Object

Class Methods

Methods Inherited

This class inherits methods from the following class −

• java.lang.Object

Example of Throwables Class

Create the following java program using any editor of your choice in say C:/> Guava.

GuavaTester.java

import java.io.IOException;

import com.google.common.base.Objects;
import com.google.common.base.Throwables;

public class GuavaTester {
   public static void main(String args[]) {
   
      GuavaTester tester = new GuavaTester();

      try {
         tester.showcaseThrowables();
         
      } catch (InvalidInputException e) {
         //get the root cause
         System.out.println(Throwables.getRootCause(e));
      
      } catch (Exception e) {
         //get the stack trace in string format
         System.out.println(Throwables.getStackTraceAsString(e));
      }

      try {
         tester.showcaseThrowables1();

      } catch (Exception e) {
         System.out.println(Throwables.getStackTraceAsString(e));
      }
   }

   public void showcaseThrowables() throws InvalidInputException {
      try {
         sqrt(-3.0);
      } catch (Throwable e) {
         //check the type of exception and throw it
         Throwables.propagateIfInstanceOf(e, InvalidInputException.class);
         Throwables.propagate(e);
      }
   }

   public void showcaseThrowables1() {
      try {
         int[] data = {1,2,3};
         getValue(data, 4);
      } catch (Throwable e) {
         Throwables.propagateIfInstanceOf(e, IndexOutOfBoundsException.class);
         Throwables.propagate(e);
      }
   }

   public double sqrt(double input) throws InvalidInputException {
      if(input < 0) throw new InvalidInputException();
      return Math.sqrt(input);
   }

   public double getValue(int[] list, int index) throws IndexOutOfBoundsException {
      return list[index];
   }

   public void dummyIO() throws IOException {
      throw new IOException();
   }
}

class InvalidInputException extends Exception {
}

Verify the Result

Compile the class using javac compiler as follows −

C:\Guava>javac GuavaTester.java

Now run the GuavaTester to see the result.

C:\Guava>java GuavaTester

See the result.

InvalidInputException
java.lang.ArrayIndexOutOfBoundsException: 4
   at GuavaTester.getValue(GuavaTester.java:52)
   at GuavaTester.showcaseThrowables1(GuavaTester.java:38)
   at GuavaTester.main(GuavaTester.java:19)

Guava - Collections Utilities

Guava introduces many advanced collections based on developers' experience in application development works. Given below is a list of useful collections −

Guava - Caching Utilities

Guava provides a very powerful memory based caching mechanism by an interface LoadingCache<K,V>. Values are automatically loaded in the cache and it provides many utility methods useful for caching needs.

Interface Declaration

Following is the declaration for com.google.common.cache.LoadingCache<K,V> interface −

@Beta
@GwtCompatible
public interface LoadingCache<K,V>
   extends Cache<K,V>, Function<K,V>

Interface Methods

Example of LoadingCache

Create the following java program using any editor of your choice in say C:/> Guava.

GuavaTester.java

import java.util.HashMap;
import java.util.Map;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.TimeUnit;

import com.google.common.base.MoreObjects;
import com.google.common.cache.CacheBuilder;
import com.google.common.cache.CacheLoader;
import com.google.common.cache.LoadingCache;

public class GuavaTester {
   public static void main(String args[]) {
   
      //create a cache for employees based on their employee id
      LoadingCache<String, Employee> employeeCache = 
         CacheBuilder.newBuilder()
         .maximumSize(100)                             // maximum 100 records can be cached
         .expireAfterAccess(30, TimeUnit.MINUTES)      // cache will expire after 30 minutes of access
         .build(new CacheLoader<String, Employee>() {  // build the cacheloader
            
            @Override
            public Employee load(String empId) throws Exception {
               //make the expensive call
               return getFromDatabase(empId);
            } 
         });

      try {			
         //on first invocation, cache will be populated with corresponding
         //employee record
         System.out.println("Invocation #1");
         System.out.println(employeeCache.get("100"));
         System.out.println(employeeCache.get("103"));
         System.out.println(employeeCache.get("110"));
         
         //second invocation, data will be returned from cache
         System.out.println("Invocation #2");
         System.out.println(employeeCache.get("100"));
         System.out.println(employeeCache.get("103"));
         System.out.println(employeeCache.get("110"));

      } catch (ExecutionException e) {
         e.printStackTrace();
      }
   }

   private static Employee getFromDatabase(String empId) {
   
      Employee e1 = new Employee("Mahesh", "Finance", "100");
      Employee e2 = new Employee("Rohan", "IT", "103");
      Employee e3 = new Employee("Sohan", "Admin", "110");

      Map<String, Employee> database = new HashMap<String, Employee>();
      
      database.put("100", e1);
      database.put("103", e2);
      database.put("110", e3);
      
      System.out.println("Database hit for" + empId);
      
      return database.get(empId);		
   }
}

class Employee {
   String name;
   String dept;
   String emplD;

   public Employee(String name, String dept, String empID) {
      this.name = name;
      this.dept = dept;
      this.emplD = empID;
   }
   
   public String getName() {
      return name;
   }
   
   public void setName(String name) {
      this.name = name;
   }
   
   public String getDept() {
      return dept;
   }
   
   public void setDept(String dept) {
      this.dept = dept;
   }
   
   public String getEmplD() {
      return emplD;
   }
   
   public void setEmplD(String emplD) {
      this.emplD = emplD;
   }

   @Override
   public String toString() {
      return MoreObjects.toStringHelper(Employee.class)
      .add("Name", name)
      .add("Department", dept)
      .add("Emp Id", emplD).toString();
   }	
}

Verify the Result

Compile the class using javac compiler as follows −

C:\Guava>javac GuavaTester.java

Now run the GuavaTester to see the result.

C:\Guava>java GuavaTester

See the result.

Invocation #1
Database hit for100
Employee{Name=Mahesh, Department=Finance, Emp Id=100}
Database hit for103
Employee{Name=Rohan, Department=IT, Emp Id=103}
Database hit for110
Employee{Name=Sohan, Department=Admin, Emp Id=110}
Invocation #2
Employee{Name=Mahesh, Department=Finance, Emp Id=100}
Employee{Name=Rohan, Department=IT, Emp Id=103}
Employee{Name=Sohan, Department=Admin, Emp Id=110}

Guava - String Utilities

Guava introduces many advanced string utilities based on developers' experience in application development works. Following is the list of useful string based utilities −

Guava - Primitive Utilities

As primitive types of Java cannot be used to pass in generics or in collections as input, Guava provided a lot of Wrapper Utilities classes to handle primitive types as Objects. Following is the list of useful primitive processing utilities −

Guava - Math Utilities

Guava provides Mathematics related Utilities classes to handle int, long and BigInteger. Following is the list of useful utilities −