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Decision Making in Java (if, if-else, switch, break, continue, jump)
Decision Making in programming is similar to decision making in real life. In programming also we face some situations where we want a certain block of code to be executed when some condition is fulfilled.
A programming language uses control statements to control the flow of execution of program based on certain conditions. These are used to cause the flow of execution to advance and branch based on changes to the state of a program.
Java’s Selection statements:
- if
- if-else
- nested-if
- if-else-if
- switch-case
- jump – break, continue,return
if condition
This logic is really simple. if the condition return true then execute the code block.
if(condition){
//statement to execute if condition is true
}
Look at the example below since a<b is true then the code inside the curly braces will be executed.
public static void showIf() {
int a = 10;
int b = 20;
if (a < b) {
System.out.println("a<b is true");
}
}
The output is:
a<b is true
if-else condition
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.
if (condition)
{
// Executes this block if
// condition is true
}
else
{
// Executes this block if
// condition is false
}
The output below will be a<b is false since a<b is false.
public static void showIfElse() {
int a = 100;
int b = 20;
if (a < b) {
System.out.println("a<b is true");
} else {
System.out.println("a<b is false");
}
}
nested-if
nested-if:
A nested if is an if statement that is the target of another if or else. Nested if statements means 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
}
}
Code below will print a<b is true.
public static void showNestedIf() {
int a = 10;
int b = 20;
if (a == 10) {
if (a < b) {
System.out.println("a<b is true");
} else {
System.out.println("a<b is false");
}
}
}
if-else-if
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;
Code below will print a==10
public static void showIfElseIf() {
int a = 10;
if (a == 1) {
System.out.println("a==1");
} else if (a == 2) {
System.out.println("a==2");
} else if (a == 3) {
System.out.println("a==3");
} else {
System.out.println("a==10");
}
}
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;
}
- Expression can be of type byte, short, int char or an enumeration. Beginning with JDK7, expression can also be of type String.
- Dulplicate 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.
Code below will print Switch demo a==20.
public static void showSwitch() {
int a = 20;
switch (a) {
case 1:
System.out.println("a==1");
break;
case 2:
System.out.println("a==2");
break;
case 3:
System.out.println("a==3");
break;
default:
System.out.println("Switch demo a==20");
}
}
jump:
Java supports three jump statement:
- break
- continue
- return
. These three statements transfer control to other part of the program.
- Break:=
In Java, 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.
Using break to exit a Loop
Using break, we can force immediate termination of a loop, bypassing the conditional expression and any remaining code in the body of the loop.
Note: Break, when used inside a set of nested loops, will only break out of the innermost loop.
Code below won’t loop 100 times since a==10 will break the loop and print Since a==10 then break the loop.
public static void showJumpBreak() {
int a = 10;
for (int i = 0; i < 100; i++) {
if (a == 10) {
System.out.println("Since a==10 then break the loop");
break;
}
}
}
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.
Code below print odd number. Since we just wanna odd number so if the number is not odd then we don’t need to run the rest of the code then we just leave this loop and enter the next one.
It will print 1 3 5 7 9.
public static void showJumpContinue() {
int a = 10;
for (int i = 0; i < 10; i++) {
if (i % 2 == 0) {
continue;
}
// If number is odd, print it
System.out.print(i + " ");
}
}
Return:The return statement is used to explicitly return from a method. That is, it causes a program control to transfer back to the caller of the method.
Code below shows the return keyword usage since if statement will be executed so the code
System.out.println("This won't execute."); will not executed.
public static void showJumpReturn() {
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.");
}