Android project initiated

src/org/solovyev/util/StringUtils.java

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+package org.solovyev.util;
+
+import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
+
+public class StringUtils {
+
+	public static boolean isEmpty ( @Nullable String s ){
+		return s == null || s.length() == 0;
+	}
+	
+	@NotNull
+	public static String getNotEmpty ( @Nullable String s, @NotNull String defaultValue ){
+		return isEmpty(s) ? defaultValue : s;
+	}
+}
+

src/org/solovyev/util/date/DateUtils.java

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+package org.solovyev.util.date;
+
+public class DateUtils {
+	
+	public static long MS_IN_SECONDS = 1000l;
+	
+	public static long msToSeconds (long ms) {
+		return ms / 1000l;
+	}
+
+}

src/org/solovyev/util/math/MathEntity.java

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+package org.solovyev.util.math;
+
+import org.jetbrains.annotations.NotNull;
+
+public enum MathEntity {
+
+	minus("-"),
+	equals("="),
+	factorial("!"),
+	plus("+"),
+	multiply("*"),
+	divide("/"),
+	power("^"),
+	sin("sin"),
+	asin("asin"),
+	cos("cos"),
+	acos("acos"),
+	tg("tg"),
+	atg("atg"),
+	exp("exp"),
+	log("log"),
+	ln("ln"),
+	mod("mod"),
+	sqrt("sqrt");
+		
+	@NotNull
+	private final String text;
+	
+	private MathEntity (@NotNull String text) {
+		this.text = text;
+	}
+
+	@NotNull
+	public String getText() {
+		return text;
+	}
+}

src/org/solovyev/util/math/MathEntityType.java

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+package org.solovyev.util.math;
+
+import java.util.Arrays;
+import java.util.List;
+
+import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
+
+public enum MathEntityType {
+
+	digit,
+	function, 
+	unary_operation,
+	binary_operation,
+	group_symbols,
+	group_symbol;
+	
+	private static final List<Character> unaryOperations = Arrays.asList('-', '=', '!');
+	
+	private static final List<Character> binaryOperations = Arrays.asList('-', '+', '*', '/', '^' );
+
+	private static final List<String> functions = Arrays.asList("sin", "asin", "cos", "acos", "tg", "atg", "exp", "log", "ln", "mod", "sqrt");
+	
+	private static final List<String> groupSymbols = Arrays.asList("[]", "()", "{}");
+
+	private static final List<Character> singleGroupSymbols = Arrays.asList('[', ']', '(', ')', '{', '}');
+	
+	@Nullable
+	public static MathEntityType getType( @NotNull String s ) {
+		MathEntityType result = null;
+		
+		if ( s.length() == 1 ) {
+			char ch = s.charAt(0);
+			
+			if ( Character.isDigit(ch) ) {
+				result = MathEntityType.digit;
+			} else if ( unaryOperations.contains(ch) ) {
+				result = MathEntityType.unary_operation; 
+			} else if ( binaryOperations.contains(ch) ) {
+				result = MathEntityType.binary_operation; 
+			} else if ( singleGroupSymbols.contains(ch) ) {
+				result = MathEntityType.group_symbol;
+			}
+		}
+		
+		if ( result == null ) {
+			if ( functions.contains(s) ) {
+				result = MathEntityType.function;
+			} else if ( groupSymbols.contains(s) ) {
+				result = MathEntityType.group_symbols;
+			}
+		}
+		
+		
+		return result;
+	}
+}

src/org/solovyev/util/math/MathUtils.java

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+package org.solovyev.util.math;
+
+import org.jetbrains.annotations.NotNull;
+
+public class MathUtils {
+
+	public static float getDistance(@NotNull Point2d startPoint,
+			@NotNull Point2d endPoint) {
+		return getNorm(subtract(endPoint, startPoint));
+	}
+
+	public static Point2d subtract(@NotNull Point2d p1, @NotNull Point2d p2) {
+		return new Point2d(p1.getX() - p2.getX(), p1.getY() - p2.getY());
+	}
+	
+	public static Point2d sum(@NotNull Point2d p1, @NotNull Point2d p2) {
+		return new Point2d(p1.getX() + p2.getX(), p1.getY() + p2.getY());
+	}
+
+	public static float getNorm(@NotNull Point2d point) {
+		return (float) Math.pow(
+				Math.pow(point.getX(), 2) + Math.pow(point.getY(), 2), 0.5);
+	}
+
+	public static float getAngle(@NotNull Point2d startPoint,
+			@NotNull Point2d axisEndPoint, @NotNull Point2d endPoint) {
+		final Point2d axisVector = subtract(axisEndPoint, startPoint);
+		final Point2d vector = subtract(endPoint, startPoint);
+
+		double a_2 = Math.pow(getDistance(vector, axisVector), 2);
+		double b = getNorm(vector);
+		double b_2 = Math.pow(b, 2);
+		double c = getNorm(axisVector);
+		double c_2 = Math.pow(c, 2);
+
+		return (float) Math.acos((-a_2 + b_2 + c_2) / (2 * b * c));
+	}
+
+}

src/org/solovyev/util/math/Point2d.java

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+package org.solovyev.util.math;
+
+public class Point2d {
+	
+	private float x = 0;
+	
+	private float y = 0;
+	
+	public Point2d() {
+	}
+	
+	public Point2d( float x, float y ) {
+		this.x = x;
+		this.y = y;
+	}
+
+	public float getX() {
+		return x;
+	}
+
+	public void setX(float x) {
+		this.x = x;
+	}
+
+	public float getY() {
+		return y;
+	}
+
+	public void setY(float y) {
+		this.y = y;
+	}
+
+	@Override
+	public String toString() {
+		return "Point2d [x=" + x + ", y=" + y + "]";
+	}
+}