Why is there no function Stream.flatMap()? [closed] - java

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Why is there no function Stream.flatMap() (without any parameters) to flatten a Stream<Stream<T>>?
It would simply be implemented as Stream.flatMap(o -> o).
In my opinion, this is by far the most common use of flatMap(Function mapper).

I would imagine because it's trivial to use
import static java.util.function.Function.identity;
...
streamOfStreams.flatMap(identity())

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Best way to write Java 8 map statement that returns constant value [closed]

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I have the following statement. The map always returned "Closed". But I think this statement s -> "CLOSED" could be rewritten using a better style.
Is there any better way to represent this?
String status = myOptional.map(s -> "CLOSED").orElse("OPEN");
Just use a ternary operatory to check for its presence :
String status = myOptional.isPresent() ? "CLOSED" : "OPEN";

Write a program in Java though array and pop up element after multiplication [closed]

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Inputs ={6,7,8,9,10}
Outputs ={42,56,72,90}
Multiplication needs to be done
// arr[ ] = {6*7,7*8,8*9,9*10}
for i--> input.length
Outputs[i] = input[i]*input[i+1]

Why can't the compiler warn against this programming error? [closed]

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If I write the following code:
int a = 5;
if (a == 1 || a == 1) {
// do something
}
Why can't the compiler point out that the second part of the if statement is unnecessary, or warn that the programmer has likely made a mistake?
The compiler does not do it. But the IDE might detect the underlying problem. For example:

Naming conventions for constants in Java [closed]

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When a constant variable ends with a number, do you need to put an underscore in between the number and the rest of the variable?
I haven't found a Java naming convention for this case.
For example YELLOW3 or YELLOW_3

Java BigInteger OR function [closed]

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I am using Java and have some problems.
I made two BigInteger variables, p and q.
In my code, I want to add if function, like if(p=1 \ q=1).
I tried many ways but there was error. Do you know how to solve this?
Your question is not completely clear, but you need to use the BigInteger.equals() method, as in this example:
if (BigInteger.equals(p, BigInteger.ONE) || BigInteger.equals(q, BigInteger.ONE)) {
// do something
}

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