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jshell> s = """
...> test
...> test
...> """
s ==> "test¥ntest¥n"
jshell> s = """
...> test
...> test
...> """
s ==> " test¥n test¥n"
jshell> s = """
...> test
...> test
...> """
s ==> "test¥n test¥n"
jshell> s = """
...> test
...> test
...> """
s ==> " test¥n test¥n"
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3 ( 4 ) ) )3
•
•
IntStream.rangeClosed(1, 20)
.mapToObj(i -> switch(i % 15) {
case 3, 6, 9, 12 -> "Fizz";
case 5,10 -> "Buzz";
case 0 -> "FizzBuzz";
default -> i + "";
})
.map(FizzBuzz::makeStr)
.forEach(System.out::print);
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3 ( 4 ) ) )3
• 1 2
var result = switch (i % 15) {
case 3, 6, 9, 12:
yield "Fizz";
case 5, 10:
yield "Buzz";
case 0:
yield "FizzBuzz";
default:
yield i + "";
}
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3 5
•
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1 3
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• .
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• ( D B
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var s = """
select *
from %1$s join %2$s on %1$s_id=%2$s_id
""".formatted("product", "category");
"from product join category on product_id=category_id"
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) (
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3
•
jshell> String s = null
s ==> null
jshell> s.length()
|
java.lang.NullPointerException
| at (#7:1)
jshell> String s = null
s ==> null
jshell> s.length()
|
java.lang.NullPointerException
| Cannot invoke method ‘length’ because ‘s’ is null
| at (#7:1)
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) ( ) )
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record Leaf(int val) {}
var l = new Leaf(3);
System.out.println(l.val());
System.out.println(l);
3
Leaf[val=3]
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( ) 0
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sealed interface Node permits Branch, Leaf {}
record Branch(Node left, Node right) implements Node {}
record Leaf(Integer val) implements Node {}
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)0 ( 0 ()
0)3 )
•
static int sum(Node n) {
if (n instanceof Branch b) {
return sum(b.left()) + sum(b.right());
} else if (n instanceof Leaf l) {
return l.val();
} else {
return 0;
}
}
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( ) 66 2 1 6 02 3 806
) 70 8
• E
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static int sum(Node n) {
return switch (n) {
case Branch b -> sum(b.left()) + sum(b.right());
case Leaf l -> l.val();
}
}
return switch(n) {
case Branch(var l, var r) -> sum(l) + sum(r);
case Leaf(var v) -> v;
}
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)(
• !
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•