BE THE CODER > Tools and Libs > Google Guava Examples > Collections

Google Guava is a java library with lot of utilities and reusable components. This requires the library guava-10.0.jar to be in classpath. The following example shows using Constraints.constrainedSet() API. It returns a constrained set which enforces a specific constraint on the set.

File Name :	com/bethecoder/tutorials/guava/collection_tests/ConstrainedSetTest.java
Author :	Sudhakar KV
Email :	[email protected]


package com.bethecoder.tutorials.guava.collection_tests;



import java.util.HashSet;

import java.util.Set;



import com.bethecoder.tutorials.guava.common.Student;

import com.google.common.collect.Constraint;

import com.google.common.collect.Constraints;



public class ConstrainedSetTest {



  /**

   * @param args

   */

  public static void main(String[] args) {

    

    Student student = new Student("Sriram", 2, "Chess");

    Student student2 = new Student("Charan", 18, "Cricket");

    

    Set<Student> childStudents = Constraints.constrainedSet(

        new HashSet<Student>(), new KidConstraint());

    

    //Positive case

    childStudents.add(student);

    System.out.println(childStudents);

    

    //Negative case

    try {

      childStudents.add(student2);

    } catch (RuntimeException e) {

      System.out.println(e);

    }

  }

}



class KidConstraint implements Constraint<Student> {

  @Override

  public Student checkElement(Student element) {

    if (!element.isKid()) {

      throw new RuntimeException("This collection accepts only kids");

    }

    return element;

  }

}

Constrained Set