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Programming-Idioms

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Idiom #5 Create a 2D Point data structure

Declare a container type for two floating-point numbers x and y

 


class Point { double x, y; }

Idiom #14 Pick uniformly a random floating point number in [a..b)

Pick a random number greater than or equals to a, strictly inferior to b. Precondition : a < b.

 


double pick(double a, double b){
	return a + (Math.random() * (b-a));
}

Idiom #254 Replace value in list

Replace all exact occurrences of "foo" with "bar" in the string list x

 


x = x.stream()
     .map(s -> s.equals("foo") ? "bar" : s)
     .toList();

For many more Java snippets to curate, see the full list.

Docs & demos

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37% of the Java snippets don't have an external link to a documentation page yet. For example, these implementations would need a doc URL:

Idiom #50 Make an infinite loop

Write a loop that has no end clause.

 

while (true);

Idiom #154 Halfway between two hex color codes

Find color c, the average between colors c1, c2.

c, c1, c2 are strings of hex color codes: 7 chars, beginning with a number sign # .
Assume linear computations, ignore gamma corrections.

 

StringBuilder sb = new StringBuilder("#");
for(int i=0;i<3;i++) {
  String sub1 = c1.substring(1+2*i,3+2*i);
  String sub2 = c2.substring(1+2*i,3+2*i);
  int v1 = Integer.parseInt(sub1, 16);
  int v2 = Integer.parseInt(sub2, 16);
  int v = (v1 + v2)/2;
  String sub = String.format("%02X", v);
  sb.append(sub);
}
String c = sb.toString();

Idiom #195 Pass a two-dimensional array

Pass an array a of real numbers to the procedure (resp. function) foo. Output the size of the array, and the sum of all its elements when each element is multiplied with the array indices i and j (assuming they start from one).

 

public static void foo(int[][] a){
       System.out.println("Array a has a size of " + a.length+" by " + a[0].length);
       int sum = 0;
       for (int i = 0; i<a.length; i++){
           for (int j = 0; j<a[0].length; j++){
               sum += ((i+1)*(j+1)*a[i][j]);
           }
       }
       System.out.println("The sum of all elements multiplied by their indices is: " + sum);
    }

81% of the Java snippets don't have a runnable demo yet.

For example, these implementations would need a demo URL:

Idiom #257 Traverse list backwards

Print each index i and value x from the list items, from the last down to the first.

 

T x;
int i = items.size() - 1;
while (i != -1) {
    x = items.get(i);
    out.printf("%s %s%n", i--, x);
}

Idiom #251 Parse binary digits

Extract integer value i from its binary string representation s (in radix 2)
E.g. "1101" -> 13

 

Integer i = Integer.valueOf(s, 2);

Idiom #274 Remove all white space characters

Create the string t from the string s, removing all the spaces, newlines, tabulations, etc.

 

String t = "";
for (char c : s.toCharArray())
    if (!isWhitespace(c)) t = t + c;

Missing implementations

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A Java implementation is missing for 50 idioms out of 371 idioms.

You may help by writing a Java snippet for these idioms:


Idiom #183 Make HTTP PUT request

Make a HTTP request with method PUT to the URL u

Idiom #323 Set HTTP request header

Make an HTTP request with method GET to the URL u, with the request header "accept-encoding: gzip", then store the body of the response in the buffer data.

Idiom #268 User-defined operator

Define a type vector containing three floating point numbers x, y, and z. Write a user-defined operator x that calculates the cross product of two vectors a and b.