Java has six relational operators that compare two numbers and return a
boolean value. The relational operators are <,
>, <=, >=, ==, and
!=.
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x < y
|
Less than |
True if x is less than y, otherwise false. |
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x > y
|
Greater than |
True if x is greater than y, otherwise false. |
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x <= y
|
Less than or equal to |
True if x is less than or equal to y, otherwise
false. |
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x >= y
|
Greater than or equal to |
True if x is greater than or equal to y, otherwise
false. |
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x == y
|
Equal |
True if x equals y, otherwise false. |
|
x != y
|
Not Equal |
True if x is not equal to y, otherwise
false. |
Here are some code snippets showing the relational operators. boolean test1 = 1 < 2; // True. One is less that two.
boolean test2 = 1 > 2; // False. One is not greater than two.
boolean test3 = 3.5 != 1; // True. One does not equal 3.5
boolean test4 = 17*3.5 >= 67.0 - 42; //True. 59.5 is greater than 5
boolean test5 = 9.8*54 <= 654; // True. 529.2 is less than 654
boolean test6 = 6*4 == 3*8; // True. 24 equals 24
boolean test7 = 6*4 <= 3*8; // True. 24 is less than or equal to 24
boolean test8 = 6*4 < 3*8; // False. 24 is not less than 24
This, however, is an unusual use of booleans. Almost all use of booleans
in practice comes in conditional statements and loop tests. You've already seen
several examples of this. Earlier you saw this
if (args.length > 0) {
System.out.println("Hello " + args[0]);
}
args.length > 0 is a boolean value. In
other words it is either true or it is false. You
could write
boolean test = args.length > 0;
if (test) {
System.out.println("Hello " + args[0]);
}
instead. However in simple situations like this the original approach is
customary. Similarly the condition test in a while loop is a
boolean. When you write while (i < args.length) the i <
args.length is a boolean.
課堂練習：
寫一程式，可輸入一個介於0和100的正整數score，使用if-else
if-else語法，使得：
若score>=60，則輸出「及格」，
否則如果score>50，則輸出「補考」，
否則輸出「死當」。
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