Java

import java.util.Random;

class Main {

public static void main(String[] args) {

String[] num_methods = {"xxxValue()","compareTo()","equals()","valueOf()","toString()",

"parseInt()","abs()","ceil()"," floor()","rint()","round()","min()","max()",

"exp()","log()","pow()","sqrt()","random()"

};

String[] char_methods = {"isLetter()","isDigit()","isWhitespace()","isUpperCase()","isLowerCase()",

"toUpperCase()","toLowerCase()","toLowerCase()"

};

String[] string_methods = {"charAt(int index)","compareTo(Object o)","compareTo(String anotherString)","compareToIgnoreCase(String str)","compareToIgnoreCase(String str)",

"contentEquals(StringBuffer sb)","copyValueOf(char[] data)","copyValueOf(char[] data, int offset, int count)", "endsWith(String suffix)","equals(Object anObject)","equalsIgnoreCase(String anotherString)",

"getBytes()","getBytes(String charsetName)","getChars(int srcBegin, int srcEnd, char[] dst, int dstBegin)","hashCode()","indexOf(int ch)","intern()","lastIndexOf(int ch)","length()","matches(String regex)",

"replace(char oldChar, char newChar)","replaceAll(String regex, String replacement","replaceFirst(String regex, String replacement)","split(String regex)","startsWith(String prefix)","subSequence(int beginIndex, int endIndex)",

"substring(int beginIndex)","toCharArray()","toLowerCase()","toString()","toUpperCase()","trim()","valueOf(primitive data type x)"

};

String[] javaConcepts = {"class & objects","methods","modifiers","polymorphism","encapsulation","inheritance","interface","variable types",

"exceptions","overriding vs overloading","abstraction","constructors","basic data types","break & continue","this keyword",""

};

String[] collections = {"LinkedList","ArrayList","HashMap","TreeMap","List"

};

String[] data_str = {"static/dynamic array","stack","queue","linked list","hashmap","tree"};

Random rand = new Random();

int num_idx = rand.nextInt(num_methods.length-1);

int char_idx = rand.nextInt(char_methods.length-1);

int string_idx = rand.nextInt(string_methods.length-1);

int concept_idx = rand.nextInt(javaConcepts.length-1);

int collections_idx = rand.nextInt(collections.length-1);

int ds_index = rand.nextInt(6);

System.out.println("Java methods: ");

System.out.println("Number method: " + num_methods[num_idx] );

System.out.println("Character method: " + char_methods[char_idx] );

System.out.println("String method: " + string_methods[string_idx] );

System.out.println("Java concepts: ");

System.out.println("Concept: " + javaConcepts[concept_idx] );

System.out.println("Collections: " + collections[collections_idx] );

System.out.println("Implement: " + data_str[ds_index]);

}

}