如何使用Java 8循环和打印2D数组 [英] How to Loop and Print 2D array using Java 8
问题描述
考虑这个二维数组
String [] [] names = {{Sam,Smith},
{Robert,Delgro},
{James,Gosling},
};
使用经典方式,如果我们想要访问二维数组的每个元素,那么我们需要使用两个for循环迭代二维数组。
for(String [] a:names){
for (String s:a){
System.out.println(s);
}
}
是否有一种新的优雅方式来循环和打印2D使用Java 8特性的数组(Lambdas,方法参考,Streams,......)?
到目前为止我尝试的是:
Arrays.asList(names)。stream()。forEach(System.out :: println);
输出:
[Ljava.lang.String; @ 6ce253f1
[Ljava.lang.String; @ 53d8d10a
[Ljava.lang.String; @ e9e54c2
保持与相同的输出
loops:
Stream.of(names)
.flatMap(Stream :: of)
.forEach(System.out :: println);
(参见 流#flatMap
)
还类似于:
Arrays.stream(names)
.map(a - > String.join(,a))
.forEach(System.out :: println);
产生如下输出:
<$ p $ s> Sam Smith
Robert Delgro
James Gosling
(参见String#join$c$ c>
。)
此外:
系统.out.println(
Arrays.stream(names)
.map(a - > String.join(,a))
.collect(Collectors.joining(,) ))
);
产生如下输出:
<$ p $ Sam Smith,Robert Delgro,James Gosling
(参见 收集者#joning
。)
加入是Java 8中讨论较少但仍然很精彩的新功能之一。
Consider this two dimentional array
String[][] names = { {"Sam", "Smith"},
{"Robert", "Delgro"},
{"James", "Gosling"},
};
Using the classic way, if we want to access each element of a two dimensional array, then we need to iterate through two dimensional array using two for loops.
for (String[] a : names) {
for (String s : a) {
System.out.println(s);
}
}
Is there a new elegant way to loop and Print 2D array using Java 8 features (Lambdas,method reference,Streams,...)?
What I have tried so far is this:
Arrays.asList(names).stream().forEach(System.out::println);
Output:
[Ljava.lang.String;@6ce253f1
[Ljava.lang.String;@53d8d10a
[Ljava.lang.String;@e9e54c2
Keeping the same output as your for
loops:
Stream.of(names)
.flatMap(Stream::of)
.forEach(System.out::println);
(See Stream#flatMap
.)
Also something like:
Arrays.stream(names)
.map(a -> String.join(" ", a))
.forEach(System.out::println);
Which produces output like:
Sam Smith Robert Delgro James Gosling
(See String#join
.)
Also:
System.out.println(
Arrays.stream(names)
.map(a -> String.join(" ", a))
.collect(Collectors.joining(", "))
);
Which produces output like:
Sam Smith, Robert Delgro, James Gosling
(See Collectors#joining
.)
Joining is one of the less discussed but still wonderful new features of Java 8.
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