How do I use try-with-resources statement?

The try-with-resources statement is introduced in the Java 7. With this new statement we can simplify resource management in our program, it also known as ARM (Automatic Resource Management).

This statement is a try statement that declares one or more resources. After the program finish with the resource it must be closed. The try-with-resources ensures that each resource is closed and the end of the statement.

Any object that implements java.lang.AutoCloseable, which includes all objects which implement java.io.Closeable, can be used as a resource.

package org.kodejava.example.basic;

import java.io.*;

public class TryWithResourceExample {
    public static void main(String[] args) {
        try {
            TryWithResourceExample demo = new TryWithResourceExample();
            demo.printStream("/tmp/data.txt");
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    private void printStream(String fileName) throws IOException {
        char[] buffer = new char[1024];

        try (InputStream is = new FileInputStream(fileName);
             Reader reader = new BufferedReader(
                     new InputStreamReader(is, "UTF-8"))) {

            while (reader.read(buffer) != -1) {
                System.out.println(buffer);
            }
        }
    }
}

How do I use string in switch statement?

Starting from Java 7 release you can now use a String in the switch statement. On the previous version we can only use constants type of byte, char, short, int (and their corresponding reference / wrapper type) or enum constants in the switch statement.

The code below give you a simple example on how the Java 7 extended to allow the use of String in switch statement.

package org.kodejava.example.basic;

public class StringInSwitchExample {
    public static void main(String[] args) {
        String day = "Sunday";
        switch (day) {
            case "Sunday":
                System.out.println("doSomething");
                break;
            case "Monday":
                System.out.println("doSomethingElse");
                break;
            case "Tuesday":
            case "Wednesday":
                System.out.println("doSomeOtherThings");
                break;
            default:
                System.out.println("doDefault");
                break;
        }
    }
}

How do I use the || operator in Java?

The || operator or conditional OR operator operates on two boolean expressions. This operator exhibit “short-circuiting” behavior, which means that the second operand is evaluated only if needed.

The || operator evaluate only boolean values. For an OR (||) expression it will return true if either of the operand is true. If the first operand resolves true, then the second operand will not evaluated, because the complete expression will return true.

package org.kodejava.example.fundamental;

public class ConditionalORDemo {
    public static void main(String[] args) {
        // the second operand (5<3) is not evaluated, because the
        // first operand return true, the result of complete
        // expression will be true
        boolean a = (1 == 1) || (5 < 3);

        // the first operand return false, the second operand is
        // evaluated to check the result of the second expression.
        // If the second operand resolves to true, the complete
        // expression return true, otherwise return false.
        boolean b = (5 < 3) || (2 == 3);
        boolean c = (5 < 3) || (1 == 1);

        System.out.println("result a: " + a);
        System.out.println("result b: " + b);
        System.out.println("result c: " + c);
    }
}

The program prints the following output:

result a: true
result b: false
result c: true

How do I use the boolean negation (!) operator in Java?

The ! operator is a logical compliment operator. The operator inverts the value of a boolean expression.

package org.kodejava.example.fundamental;

public class NegationOperator {
    public static void main(String[] args) {
        // negate the result of boolean expressions
        boolean negate = !(2 < 3);
        boolean value = !false;

        System.out.println("result: " + negate);
        System.out.println("value : " + value);
    }
}

Here is the result of the program:

result: false
value : true

What is reference variable in Java?

The only way you can access an object is through a reference variable. A reference variable is declared to be of a specific type and that type can never be changed. Reference variables can be declared as static variables, instance variables, method parameters, or local variables.

A reference variable that is declared as final can’t never be reassigned to refer to a different object. The data within the object can be modified, but the reference variable cannot be changed.

package org.kodejava.example.basic;

public class ReferenceDemo {
    public static void main(String[] args) {
        // Declaration of Reference variable
        Reference ref1, ref2;

        // ref3 is declared final, ref3 can't be reassigned
        // or refer to different object
        final Reference ref3;

        // assign ref1 with object Reference
        ref1 = new Reference("This is the first reference variable", 1);

        // access method getNumber() of object Reference through
        // variable ref1
        int number = ref1.getNumber();
        System.out.println("number= " + number);

        // assign ref2 with object Reference
        ref2 = new Reference("This is the second reference variable", 2);

        // passing ref2 as method parameter of printText() method
        ReferenceDemo.printText(ref2);

        // assign ref3 with object Reference
        ref3 = new Reference("This is the third reference variable", 3);

        // try to reassign ref3 will cause a compile-time error
        // ref3 = new Reference("Try to reassign", 3);

    }

    public static void printText(Reference reference) {
        String text = reference.getText();
        System.out.println(text);
    }
}
package org.kodejava.example.basic;

public class Reference {
    private int number;
    private String text;

    Reference(String text, int number) {
        this.text = text;
        this.number = number;
    }

    public String getText() {
        return text;
    }

    public int getNumber() {
        return number;
    }
}