Java tutorial
/* * Licensed to the Apache Software Foundation (ASF) under one or more * contributor license agreements. See the NOTICE file distributed with * this work for additional information regarding copyright ownership. * The ASF licenses this file to You under the Apache License, Version 2.0 * (the "License"); you may not use this file except in compliance with * the License. You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ package org.apache.wicket.util.lang; import java.lang.reflect.Array; import java.math.BigDecimal; import java.math.BigInteger; import java.util.HashMap; /** * Object utilities. * * @author Jonathan Locke */ public final class Objects { /** Type tag meaning java.math.BigDecimal. */ private static final int BIGDEC = 9; /** Type tag meaning java.math.BigInteger. */ private static final int BIGINT = 6; /** Type tag meaning boolean. */ private static final int BOOL = 0; /** Type tag meaning byte. */ private static final int BYTE = 1; /** Type tag meaning char. */ private static final int CHAR = 2; /** Type tag meaning double. */ private static final int DOUBLE = 8; /** Type tag meaning float. */ private static final int FLOAT = 7; /** Type tag meaning int. */ private static final int INT = 4; /** Type tag meaning long. */ private static final int LONG = 5; /** * The smallest type tag that represents reals as opposed to integers. You can see whether a * type tag represents reals or integers by comparing the tag to this constant: all tags less * than this constant represent integers, and all tags greater than or equal to this constant * represent reals. Of course, you must also check for NONNUMERIC, which means it is not a * number at all. */ private static final int MIN_REAL_TYPE = FLOAT; /** Type tag meaning something other than a number. */ private static final int NONNUMERIC = 10; /** Type tag meaning short. */ private static final int SHORT = 3; /** defaults for primitives. */ private static final HashMap<Class<?>, Object> primitiveDefaults = Generics.newHashMap(); static { primitiveDefaults.put(Boolean.TYPE, Boolean.FALSE); primitiveDefaults.put(Byte.TYPE, (byte) 0); primitiveDefaults.put(Short.TYPE, (short) 0); primitiveDefaults.put(Character.TYPE, (char) 0); primitiveDefaults.put(Integer.TYPE, 0); primitiveDefaults.put(Long.TYPE, 0L); primitiveDefaults.put(Float.TYPE, 0.0f); primitiveDefaults.put(Double.TYPE, 0.0); primitiveDefaults.put(BigInteger.class, new BigInteger("0")); primitiveDefaults.put(BigDecimal.class, new BigDecimal(0.0)); } /** * Evaluates the given object as a BigDecimal. * * @param value * an object to interpret as a BigDecimal * @return the BigDecimal value implied by the given object * @throws NumberFormatException * if the given object can't be understood as a BigDecimal */ public static BigDecimal bigDecValue(final Object value) throws NumberFormatException { if (value == null) { return BigDecimal.valueOf(0L); } Class<?> c = value.getClass(); if (c == BigDecimal.class) { return (BigDecimal) value; } if (c == BigInteger.class) { return new BigDecimal((BigInteger) value); } if (c.getSuperclass() == Number.class) { return new BigDecimal(((Number) value).doubleValue()); } if (c == Boolean.class) { return BigDecimal.valueOf((Boolean) value ? 1 : 0); } if (c == Character.class) { return BigDecimal.valueOf(((Character) value).charValue()); } return new BigDecimal(stringValue(value, true)); } /** * Evaluates the given object as a BigInteger. * * @param value * an object to interpret as a BigInteger * @return the BigInteger value implied by the given object * @throws NumberFormatException * if the given object can't be understood as a BigInteger */ public static BigInteger bigIntValue(final Object value) throws NumberFormatException { if (value == null) { return BigInteger.valueOf(0L); } Class<?> c = value.getClass(); if (c == BigInteger.class) { return (BigInteger) value; } if (c == BigDecimal.class) { return ((BigDecimal) value).toBigInteger(); } if (c.getSuperclass() == Number.class) { return BigInteger.valueOf(((Number) value).longValue()); } if (c == Boolean.class) { return BigInteger.valueOf((Boolean) value ? 1 : 0); } if (c == Character.class) { return BigInteger.valueOf((Character) value); } return new BigInteger(stringValue(value, true)); } /** * Evaluates the given object as a boolean: if it is a Boolean object, it's easy; if it's a * Number or a Character, returns true for non-zero objects; and otherwise returns true for * non-null objects. * * @param value * an object to interpret as a boolean * @return the boolean value implied by the given object */ public static boolean booleanValue(final Object value) { if (value == null) { return false; } Class<?> c = value.getClass(); if (c == Boolean.class) { return (Boolean) value; } if (c == Character.class) { return (Character) value != 0; } if (value instanceof Number) { return ((Number) value).doubleValue() != 0; } return true; // non-null } /** * Compares two objects for equality, even if it has to convert one of them to the other type. * If both objects are numeric they are converted to the widest type and compared. If one is * non-numeric and one is numeric the non-numeric is converted to double and compared to the * double numeric value. If both are non-numeric and Comparable and the types are compatible * (i.e. v1 is of the same or superclass of v2's type) they are compared with * Comparable.compareTo(). If both values are non-numeric and not Comparable or of incompatible * classes this will throw and IllegalArgumentException. * * @param v1 * First value to compare * @param v2 * second value to compare * * @return integer describing the comparison between the two objects. A negative number * indicates that v1 < v2. Positive indicates that v1 > v2. Zero indicates v1 == v2. * * @throws IllegalArgumentException * if the objects are both non-numeric yet of incompatible types or do not implement * Comparable. */ @SuppressWarnings({ "unchecked", "rawtypes" }) public static int compareWithConversion(final Object v1, final Object v2) { int result; if (v1 == v2) { result = 0; } else { int t1 = getNumericType(v1), t2 = getNumericType(v2), type = getNumericType(t1, t2, true); switch (type) { case BIGINT: result = bigIntValue(v1).compareTo(bigIntValue(v2)); break; case BIGDEC: result = bigDecValue(v1).compareTo(bigDecValue(v2)); break; case NONNUMERIC: if ((t1 == NONNUMERIC) && (t2 == NONNUMERIC)) { if ((v1 instanceof Comparable) && v1.getClass().isAssignableFrom(v2.getClass())) { result = ((Comparable) v1).compareTo(v2); break; } else { throw new IllegalArgumentException("invalid comparison: " + v1.getClass().getName() + " and " + v2.getClass().getName()); } } // else fall through case FLOAT: case DOUBLE: double dv1 = doubleValue(v1), dv2 = doubleValue(v2); return (dv1 == dv2) ? 0 : ((dv1 < dv2) ? -1 : 1); default: long lv1 = longValue(v1), lv2 = longValue(v2); return (lv1 == lv2) ? 0 : ((lv1 < lv2) ? -1 : 1); } } return result; } /** * Convert between basic Java types, i.e. primitives and their wrappers, numbers and strings. * <p> * This method also detects when arrays are being converted and converts the components of one * array to the type of the other. * * @param <T> * target type * @param value * an object to be converted to the given type * @param toType * class type to be converted to * @return converted value of the type given, or null if the value cannot be converted to the * given type. */ public static <T> T convertValue(final Object value, final Class<T> toType) { Object result = null; if (value != null) { /* If array -> array then convert components of array individually */ if (value.getClass().isArray() && toType.isArray()) { Class<?> componentType = toType.getComponentType(); result = Array.newInstance(componentType, Array.getLength(value)); for (int i = 0, icount = Array.getLength(value); i < icount; i++) { Array.set(result, i, convertValue(Array.get(value, i), componentType)); } } else { if ((toType == Integer.class) || (toType == Integer.TYPE)) { result = (int) longValue(value); } if ((toType == Double.class) || (toType == Double.TYPE)) { result = doubleValue(value); } if ((toType == Boolean.class) || (toType == Boolean.TYPE)) { result = booleanValue(value) ? Boolean.TRUE : Boolean.FALSE; } if ((toType == Byte.class) || (toType == Byte.TYPE)) { result = (byte) longValue(value); } if ((toType == Character.class) || (toType == Character.TYPE)) { result = (char) longValue(value); } if ((toType == Short.class) || (toType == Short.TYPE)) { result = (short) longValue(value); } if ((toType == Long.class) || (toType == Long.TYPE)) { result = longValue(value); } if ((toType == Float.class) || (toType == Float.TYPE)) { result = new Float(doubleValue(value)); } if (toType == BigInteger.class) { result = bigIntValue(value); } if (toType == BigDecimal.class) { result = bigDecValue(value); } if (toType == String.class) { result = stringValue(value); } } } else { if (toType.isPrimitive()) { result = primitiveDefaults.get(toType); } } @SuppressWarnings("unchecked") T finalResult = (T) result; return finalResult; } /** * Evaluates the given object as a double-precision floating-point number. * * @param value * an object to interpret as a double * @return the double value implied by the given object * @throws NumberFormatException * if the given object can't be understood as a double */ public static double doubleValue(final Object value) throws NumberFormatException { if (value == null) { return 0.0; } Class<?> c = value.getClass(); if (c.getSuperclass() == Number.class) { return ((Number) value).doubleValue(); } if (c == Boolean.class) { return (Boolean) value ? 1 : 0; } if (c == Character.class) { return (Character) value; } String s = stringValue(value, true); return (s.length() == 0) ? 0.0 : Double.parseDouble(s); } /** * Returns true if a and b are equal. Either object may be null. * * @param a * Object a * @param b * Object b * @return True if the objects are equal */ public static boolean equal(final Object a, final Object b) { if (a == b) { return true; } if ((a != null) && (b != null) && a.equals(b)) { return true; } return false; } /** * Returns the constant from the NumericTypes interface that best expresses the type of an * operation, which can be either numeric or not, on the two given types. * * @param t1 * type of one argument to an operator * @param t2 * type of the other argument * @param canBeNonNumeric * whether the operator can be interpreted as non-numeric * @return the appropriate constant from the NumericTypes interface */ public static int getNumericType(int t1, int t2, final boolean canBeNonNumeric) { if (t1 == t2) { return t1; } if (canBeNonNumeric && ((t1 == NONNUMERIC) || (t2 == NONNUMERIC) || (t1 == CHAR) || (t2 == CHAR))) { return NONNUMERIC; } if (t1 == NONNUMERIC) { t1 = DOUBLE; // Try to interpret strings as doubles... } if (t2 == NONNUMERIC) { t2 = DOUBLE; // Try to interpret strings as doubles... } if (t1 >= MIN_REAL_TYPE) { if (t2 >= MIN_REAL_TYPE) { return Math.max(t1, t2); } if (t2 < INT) { return t1; } if (t2 == BIGINT) { return BIGDEC; } return Math.max(DOUBLE, t1); } else if (t2 >= MIN_REAL_TYPE) { if (t1 < INT) { return t2; } if (t1 == BIGINT) { return BIGDEC; } return Math.max(DOUBLE, t2); } else { return Math.max(t1, t2); } } /** * Returns a constant from the NumericTypes interface that represents the numeric type of the * given object. * * @param value * an object that needs to be interpreted as a number * @return the appropriate constant from the NumericTypes interface */ public static int getNumericType(final Object value) { if (value != null) { Class<?> c = value.getClass(); if (c == Integer.class) { return INT; } if (c == Double.class) { return DOUBLE; } if (c == Boolean.class) { return BOOL; } if (c == Byte.class) { return BYTE; } if (c == Character.class) { return CHAR; } if (c == Short.class) { return SHORT; } if (c == Long.class) { return LONG; } if (c == Float.class) { return FLOAT; } if (c == BigInteger.class) { return BIGINT; } if (c == BigDecimal.class) { return BIGDEC; } } return NONNUMERIC; } /** * Returns the constant from the NumericTypes interface that best expresses the type of a * numeric operation on the two given objects. * * @param v1 * one argument to a numeric operator * @param v2 * the other argument * @return the appropriate constant from the NumericTypes interface */ public static int getNumericType(final Object v1, final Object v2) { return getNumericType(v1, v2, false); } /** * Returns the constant from the NumericTypes interface that best expresses the type of an * operation, which can be either numeric or not, on the two given objects. * * @param v1 * one argument to an operator * @param v2 * the other argument * @param canBeNonNumeric * whether the operator can be interpreted as non-numeric * @return the appropriate constant from the NumericTypes interface */ public static int getNumericType(final Object v1, final Object v2, final boolean canBeNonNumeric) { return getNumericType(getNumericType(v1), getNumericType(v2), canBeNonNumeric); } /** * Returns true if object1 is equal to object2 in either the sense that they are the same object * or, if both are non-null if they are equal in the <CODE>equals()</CODE> sense. * * @param object1 * First object to compare * @param object2 * Second object to compare * * @return true if v1 == v2 */ public static boolean isEqual(final Object object1, final Object object2) { boolean result = false; if (object1 == object2) { result = true; } else { if ((object1 != null) && object1.getClass().isArray()) { if ((object2 != null) && object2.getClass().isArray() && (object2.getClass() == object1.getClass())) { result = (Array.getLength(object1) == Array.getLength(object2)); if (result) { for (int i = 0, icount = Array.getLength(object1); result && (i < icount); i++) { result = isEqual(Array.get(object1, i), Array.get(object2, i)); } } } } else { // Check for converted equivalence first, then equals() // equivalence result = (object1 != null) && (object2 != null) && ((compareWithConversion(object1, object2) == 0) || object1.equals(object2)); } } return result; } /** * Evaluates the given object as a long integer. * * @param value * an object to interpret as a long integer * @return the long integer value implied by the given object * @throws NumberFormatException * if the given object can't be understood as a long integer */ public static long longValue(final Object value) throws NumberFormatException { if (value == null) { return 0L; } Class<?> c = value.getClass(); if (c.getSuperclass() == Number.class) { return ((Number) value).longValue(); } if (c == Boolean.class) { return (Boolean) value ? 1 : 0; } if (c == Character.class) { return (Character) value; } return Long.parseLong(stringValue(value, true)); } /** * Returns a new Number object of an appropriate type to hold the given integer value. The type * of the returned object is consistent with the given type argument, which is a constant from * the NumericTypes interface. * * @param type * the nominal numeric type of the result, a constant from the NumericTypes interface * @param value * the integer value to convert to a Number object * @return a Number object with the given value, of type implied by the type argument */ public static Number newInteger(final int type, final long value) { switch (type) { case BOOL: case CHAR: case INT: return (int) value; case FLOAT: return (float) value; case DOUBLE: return (double) value; case LONG: return value; case BYTE: return (byte) value; case SHORT: return (short) value; default: return BigInteger.valueOf(value); } } /** * Evaluates the given object as a String. * * @param value * an object to interpret as a String * @return the String value implied by the given object as returned by the toString() method, or * "null" if the object is null. */ public static String stringValue(final Object value) { return stringValue(value, false); } /** * returns hashcode of the objects by calling obj.hashcode(). safe to use when obj is null. * * @param obj * @return hashcode of the object or 0 if obj is null */ public static int hashCode(final Object... obj) { if ((obj == null) || (obj.length == 0)) { return 0; } int result = 37; for (int i = obj.length - 1; i > -1; i--) { result = 37 * result + (obj[i] != null ? obj[i].hashCode() : 0); } return result; } /** * Evaluates the given object as a String and trims it if the trim flag is true. * * @param value * an object to interpret as a String * @param trim * whether to trim the string * @return the String value implied by the given object as returned by the toString() method, or * "null" if the object is null. */ public static String stringValue(final Object value, final boolean trim) { String result; if (value == null) { result = "null"; } else { result = value.toString(); if (trim) { result = result.trim(); } } return result; } /** * Returns the original object if this one is != null. If the original object is null * the default one is returned. The default object has no restriction, it might be itself null. * * @param originalObj * the original object * @param defaultObj * the default object * @return the original object if not null, the default one otherwise. */ public static <T> T defaultIfNull(T originalObj, T defaultObj) { return originalObj != null ? originalObj : defaultObj; } /** * Instantiation not allowed */ private Objects() { } }