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Another way to simulate the use of multiple if statements is with the switch statement. Take a look at the following if-else code, and notice how confusing it can be to have nested if tests, even just a few levels deep:
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int x = 3; if(x == 1) { System.out.println("x equals 1"); } else if(x == 2) { System.out.println("x equals 2"); } else if(x == 3) { System.out.println("x equals 3"); } else { System.out.println("No idea what x is"); }
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Illegal Arguments to if int x = 1; if (x) { } if (0) { } if (x = 6)
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4: Flow Control, Exceptions, and Assertions
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Now let s see the same functionality represented in a switch construct:
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int x = 3; switch (x) { case 1: System.out.println("x is equal to break; case 2: System.out.println("x is equal to break; case 3: System.out.println("x is equal to break; default: System.out.println("Still no idea }
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1");
2");
3");
what x is");
Legal Arguments to switch and case
The only type that a switch can evaluate is the primitive int! That means only variables and valuables that can be automatically promoted (in other words, implicitly cast) to an int are acceptable. So you can switch on any of the following, but nothing else:
byte short char int
You won t be able to compile if you use anything else, including the remaining numeric types of long, float, and double. The only argument a case can evaluate is one of the same type as switch can use, with one additional and big constraint: the case argument must be final! The case argument has to be resolved at compile time, so that means you can use only a literal or final variable. Also, the switch can only check for equality. This means that the other relational operators such as greater than are rendered unusable in a case. The following is an example of a valid expression using a method invocation in a switch statement. Note that for this code to be legal, the method being invoked on the object reference must return a value compatible with an int.
String s = "xyz"; switch (s.length()) { case 1:
Writing Code Using if and switch Statements (Exam Objective 2.1)
System.out.println("length is one"); break; case 2: System.out.println("length is two"); break; case 3: System.out.println("length is three"); break; default: System.out.println("no match"); }
The following example uses final variables in a case statement. Note that if the final keyword is omitted, this code will not compile.
final int one = 1; final int two = 2; int x = 1; switch (x) { case one: System.out.println("one"); break; case two: System.out.println("two"); break; }
One other rule you might not expect involves the question, What happens if I switch on a variable smaller than an int Look at the following switch example:
byte g = 2; switch(g) { case 23: case 128: }
This code won t compile. Although the switch argument is legal a byte is implicitly cast to an int the second case argument (128) is too large for a byte, and the compiler knows it! Attempting to compile the preceding example gives you an error:
Test.java:6: possible loss of precision found : int required: byte case 129: ^
4: Flow Control, Exceptions, and Assertions
It s also illegal to have more than one case label using the same value. For example, the following block of code won t compile because it uses two cases with the same value of 80:
int temp = 90; switch(temp) { case 80 : System.out.println("80"); break; case 80 : System.out.println("80"); break; case 90: System.out.println("90"); break; default: System.out.println("default"); }
Look for any violation of the rules for switch and case arguments. For example, you might find illegal examples like the following three snippets:
Integer in = new Integer(4); switch (in) { } ================== switch(x) { case 0 { y = 7; } } ================== switch(x) { 0: { } 1: { } }
In the first example, you can t switch on an Integer object, only an int primitive. In the second example, the case uses a curly brace and omits the colon. The third example omits the keyword case.
Writing Code Using if and switch Statements (Exam Objective 2.1)
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