Initial data commit

Task/First-class-functions/Java/first-class-functions-1.java

@@ -0,0 +1,70 @@
+import java.util.ArrayList;
+
+public class FirstClass{
+	
+	public interface Function<A,B>{
+		B apply(A x);
+	}
+	
+	public static <A,B,C> Function<A, C> compose(
+			final Function<B, C> f, final Function<A, B> g) {
+		return new Function<A, C>() {
+			@Override public C apply(A x) {
+				return f.apply(g.apply(x));
+			}
+		};
+	}
+	
+	public static void main(String[] args){
+		ArrayList<Function<Double, Double>> functions =
+			new ArrayList<Function<Double,Double>>();
+		
+		functions.add(
+				new Function<Double, Double>(){
+					@Override public Double apply(Double x){
+						return Math.cos(x);
+					}
+				});
+		functions.add(
+				new Function<Double, Double>(){
+					@Override public Double apply(Double x){
+						return Math.tan(x);
+					}
+				});
+		functions.add(
+				new Function<Double, Double>(){
+					@Override public Double apply(Double x){
+						return x * x;
+					}
+				});
+		
+		ArrayList<Function<Double, Double>> inverse = new ArrayList<Function<Double,Double>>();
+		
+		inverse.add(
+				new Function<Double, Double>(){
+					@Override public Double apply(Double x){
+						return Math.acos(x);
+					}
+				});
+		inverse.add(
+				new Function<Double, Double>(){
+					@Override public Double apply(Double x){
+						return Math.atan(x);
+					}
+				});
+		inverse.add(
+				new Function<Double, Double>(){
+					@Override public Double apply(Double x){
+						return Math.sqrt(x);
+					}
+				});
+		System.out.println("Compositions:");
+		for(int i = 0; i < functions.size(); i++){
+			System.out.println(compose(functions.get(i), inverse.get(i)).apply(0.5));
+		}
+		System.out.println("Hard-coded compositions:");
+		System.out.println(Math.cos(Math.acos(0.5)));
+		System.out.println(Math.tan(Math.atan(0.5)));
+		System.out.println(Math.pow(Math.sqrt(0.5), 2));
+	}
+}