JAVA: Pengambilan Keputusan di Java

Proses pengambilan keputusan dalam pemrograman mirip dengan pengambilan keputusan dalam kehidupan nyata. Dalam pemrograman juga menghadapi beberapa situasi di mana kita ingin blok code tertentu dieksekusi ketika beberapa kondisi terpenuhi.

Sebuah bahasa pemrograman menggunakan pernyataan kontrol untuk mengontrol aliran eksekusi program berdasarkan kondisi tertentu. Ini digunakan untuk menyebabkan aliran eksekusi berjalan / maju dan bercabang berdasarkan perubahan status program.

Perintah untuk melakukan pemilihan di Java:

• if
• if-else
• nested-if
• if-else-if
• switch-case
• jump – break, continue, return

1. if:

Pernyataan if adalah pernyataan pengambilan keputusan yang paling sederhana. Ini digunakan untuk memutuskan apakah pernyataan atau blok pernyataan tertentu akan dieksekusi atau tidak, yaitu jika kondisi tertentu benar maka blok pernyataan akan dieksekusi jika tidak.

Syntax:

if(condition) 
{
   // Statements to execute if
   // condition is true
}

Di sini, kondisi setelah di evaluasi akan benar atau salah. jika pernyataan menerima nilai boolean - jika nilainya benar maka akan mengeksekusi blok perintah di bawahnya.

Jika kita tidak memberikan kurung kurawal '{' dan '}' setelah if( condition ) maka secara default pernyataan if akan menganggap pernyataan langsung berada di dalam bloknya. Sebagai contoh,

if(condition)
   statement1;
   statement2;

// Here if the condition is true, if block 
// will consider only statement1 to be inside 
// its block.
if-statement-in-java

Example:

// Java program to illustrate If statement
class IfDemo {
    public static void main(String args[])
    {
        int i = 10;

        if (i > 15)
            System.out.println("10 is less than 15");
 
        // This statement will be executed
        // as if considers one statement by default
        System.out.println("I am Not in if");
    }
}

Output

I am Not in if

2. if-else:

The if statement alone tells us that if a condition is true it will execute a block of statements and if the condition is false it won’t. But what if we want to do something else if the condition is false. Here comes the else statement. We can use the else statement with if statement to execute a block of code when the condition is false.

Syntax:

if (condition)
{
    // Executes this block if
    // condition is true
}
else
{
    // Executes this block if
    // condition is false
}
if-else-statement

Example:

// Java program to illustrate if-else statement
class IfElseDemo {
    public static void main(String args[])
    {
        int i = 10;
 
        if (i < 15)
            System.out.println("i is smaller than 15");
        else
            System.out.println("i is greater than 15");
    }
} 

Output

i is smaller than 15
Time Complexity: O(1)

Auxiliary Space : O(1)

3. nested-if:

A nested if is an if statement that is the target of another if or else. Nested if statements mean an if statement inside an if statement. Yes, java allows us to nest if statements within if statements. i.e, we can place an if statement inside another if statement.

Syntax:

if (condition1) 
{
   // Executes when condition1 is true
   if (condition2) 
   {
      // Executes when condition2 is true
   }
}

nested-if

Example:

// Java program to illustrate nested-if statement
 
class NestedIfDemo {
    public static void main(String args[])
    {
        int i = 10;
 
        if (i == 10) {
            // First if statement
            if (i < 15)
                System.out.println("i is smaller than 15");
 
            // Nested - if statement
            // Will only be executed if statement above
            // it is true
            if (i < 12)
                System.out.println(
                    "i is smaller than 12 too");
            else
                System.out.println("i is greater than 15");
        }
    }
}

Output

i is smaller than 15
i is smaller than 12 too
Time Complexity: O(1)

Auxiliary Space : O(1)

4. if-else-if ladder:

Here, a user can decide among multiple options.The if statements are executed from the top down. As soon as one of the conditions controlling the if is true, the statement associated with that if is executed, and the rest of the ladder is bypassed. If none of the conditions is true, then the final else statement will be executed.

if (condition)
    statement;
else if (condition)
    statement;
.
.
else
    statement;

if-else-if-ladder

Example:

// Java program to illustrate if-else-if ladder
 
class ifelseifDemo {
    public static void main(String args[])
    {
        int i = 20;
 
        if (i == 10)
            System.out.println("i is 10");
        else if (i == 15)
            System.out.println("i is 15");
        else if (i == 20)
            System.out.println("i is 20");
        else
            System.out.println("i is not present");
    }
}

Output

i is 20
Time Complexity: O(1)

Auxiliary Space : O(1)

5. switch-case:

The switch statement is a multiway branch statement. It provides an easy way to dispatch execution to different parts of code based on the value of the expression.

Syntax:

switch (expression)
{
  case value1:
    statement1;
    break;
  case value2:
    statement2;
    break;
  .
  .
  case valueN:
    statementN;
    break;
  default:
    statementDefault;
}

The expression can be of type byte, short, int char, or an enumeration. Beginning with JDK7, expression can also be of type String. Duplicate case values are not allowed. The default statement is optional. The break statement is used inside the switch to terminate a statement sequence. The break statement is optional. If omitted, execution will continue on into the next case.

6. jump:

Java supports three jump statements: break, continue and return. These three statements transfer control to another part of the program.

Break: In Java, a break is majorly used for: Terminate a sequence in a switch statement (discussed above). To exit a loop. Used as a “civilized” form of goto. Continue: Sometimes it is useful to force an early iteration of a loop. That is, you might want to continue running the loop but stop processing the remainder of the code in its body for this particular iteration. This is, in effect, a goto just past the body of the loop, to the loop’s end. The continue statement performs such an action.

continue-in-java

Example:

// Java program to illustrate using
// continue in an if statement
class ContinueDemo {
    public static void main(String args[])
    {
        for (int i = 0; i < 10; i++) {
            // If the number is even
            // skip and continue
            if (i % 2 == 0)
                continue;
 
            // If number is odd, print it
            System.out.print(i + " ");
        }
    }
}

Output

1 3 5 7 9  
Time Complexity: O(1)

Auxiliary Space : O(1)

Return: The return statement is used to explicitly return from a method. That is, it causes program control to transfer back to the caller of the method. Example:

// Java program to illustrate using return
class Return {
    public static void main(String args[])
    {
        boolean t = true;
        System.out.println("Before the return.");
 
        if (t)
            return;
 
        // Compiler will bypass every statement
        // after return
        System.out.println("This won't execute.");
    }
}

Output

Before the return.

Referensi

• https://www.geeksforgeeks.org/decision-making-javaif-else-switch-break-continue-jump/