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<TITLE>if/else Statement (Java Developers Almanac Example)
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<h3>e1086. if/else Statement</h3>
The <code>if</code> statement encloses some code which is executed only if a
condition is true. The general syntax of the <code>if</code> statement is:
<pre> if (<font color="#0066ff"><i>condition</i></font>) {
<font color="#0066ff"><i>body-code</i></font>
}
</pre>
The <code>if</code> statement has two parts. The <font color="#0066ff"><i>condition</i></font> is a
boolean expression which resolves to either true or false. The
<font color="#0066ff"><i>body-code</i></font> is code that will be executed only if the condition
is true. Here is an example of the <code>if</code> statement.
<pre> // Returns 0 if s is null
public int getLength(String s) {
if (s == null) {
// This line of code is execute only if s is null
return 0;
}
return s.length();
}
</pre>
The <code>if</code> statement also has an optional <code>else</code> part which
encloses some code that is executed only if the <font color="#0066ff"><i>condition</i></font> is
false. Here is the general syntax of the <code>if</code> statement with the
optional <code>else</code> part:
<pre> if (<font color="#0066ff"><i>condition</i></font>) {
<font color="#0066ff"><i>body-code</i></font>
} else {
<font color="#0066ff"><i>else-code</i></font>
}
</pre>
The <font color="#0066ff"><i>else-code</i></font> is executed only if <font color="#0066ff"><i>condition</i></font> resolves to
false. Here is an example of the <code>if</code> statement with the optional
<code>else</code> part.
<pre> // Generates a random number and prints whether it is even or odd
if ((int)(Math.random()*100)%2 == 0) {
System.out.println("The number is even");
} else {
System.out.println("The number is odd");
}
</pre>
The <font color="#0066ff"><i>else-code</i></font> part can also be another <code>if</code> statement. An
<code>if</code> statement written this way sets up a sequence of
<code>condition</code>'s, each tested one after the other in top-down
order. If one of the conditions is found to be true, the
<font color="#0066ff"><i>body-code</i></font> for that <code>if</code> statement is executed. Once
executed, no other conditions are tested and execution continues after
the sequence. Here is an example of a sequence of
<code>if</code>/<code>else</code>/<code>if</code> statements
<pre> // Converts the time, which is in milliseconds, into a
// more readable format with higher units
public String getTimeUnit(long time) {
String unit = "ms";
if (time >= 365*24*60*60*1000L) {
unit = "years";
time /= 365*24*60*60*1000L;
} else if (time >= 24*60*60*1000) {
unit = "days";
time /= 24*60*60*1000;
} else if (time >= 60*60*1000) {
unit = "hr";
time /= 60*60*1000;
} else if (time >= 60*1000) {
unit = "min";
time /= 60*1000;
} else if (time >= 1000) {
unit = "sec";
time /= 1000;
}
// Execution continues here if any of the conditions match
return time + " " + unit;
}
</pre>
Here's some sample output:
<pre> getTimeUnit(123); // 123 ms
getTimeUnit(1234)); // 1 sec
getTimeUnit(12345)); // 12 sec
getTimeUnit(123456)); // 2 min
getTimeUnit(1234567)); // 20 min
getTimeUnit(12345678)); // 3 hr
getTimeUnit(123456789)); // 1 days
getTimeUnit(1234567890)); // 14 days
getTimeUnit(12345678900L)); // 142 days
getTimeUnit(123456789000L)); // 3 years
</pre>
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<b>Related Examples</b></font></td>
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Using the \cv{for} Statement for Array Iteration [5.0]
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e1088. <a class="eglink" href="TryCatch.html?l=rel">
try/catch Statement
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e1089. <a class="eglink" href="CatchThrowable.html?l=rel">
Catching all Errors and Exceptions
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