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13 <html xmlns="http://www.w3.org/1999/xhtml">
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15 <title>Math - The Commons Math User Guide - Fractions</title>
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66
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67 <h5>User Guide</h5>
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68 <ul>
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70 <li class="none">
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71 <a href="../userguide/index.html">Contents</a>
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108 </li>
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109
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110 <li class="none">
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111 <strong>Fractions</strong>
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146 </div>
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147 <div id="bodyColumn">
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148 <div id="contentBox">
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149 <div class="section"><h2><a name="a9_Fractions"></a>9 Fractions</h2>
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150 <div class="section"><h3><a name="a9.1_Overview"></a>9.1 Overview</h3>
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151 <p>
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152 The fraction packages provides a fraction number type as well as
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153 fraction number formatting.
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154 </p>
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155 </div>
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156 <div class="section"><h3><a name="a9.2_Fraction_Numbers"></a>9.2 Fraction Numbers</h3>
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157 <p><a href="../apidocs/org/apache/commons/math/fraction/Fraction.html">
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158 org.apache.commons.math.fraction.Fraction</a> and
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159 <a href="../apidocs/org/apache/commons/math/fraction/BigFraction.html">
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160 org.apache.commons.math.fraction.BigFraction</a> provide fraction number
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161 type that forms the basis for the fraction functionality found in
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162 commons-math. The former one can be used for fractions whose numerators
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163 and denominators are small enough to fit in an int (taking care of intermediate
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164 values) while the second class should be used when there is a risk the numerator
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165 and denominator grow very large.
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166 </p>
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167 <p>
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168 A fraction number, can be built from two integer arguments representing numerator
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169 and denominator or from a double which will be approximated:
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170 <div class="source"><pre>Fraction f = new Fraction(1, 3); // 1 / 3
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171 Fraction g = new Fraction(0.25); // 1 / 4</pre>
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172 </div>
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173 </p>
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174 <p>
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175 Of special note with fraction construction, when a fraction is created it is always reduced to lowest terms.
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176 </p>
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177 <p>
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178 The <code>Fraction</code> class provides many unary and binary
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179 fraction operations. These operations provide the means to add,
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180 subtract, multiple and, divide fractions along with other functions similar to the real number functions found in
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181 <code>java.math.BigDecimal</code>:
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182 <div class="source"><pre>Fraction lhs = new Fraction(1, 3);
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183 Fraction rhs = new Fraction(2, 5);
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184
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185 Fraction answer = lhs.add(rhs); // add two fractions
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186 answer = lhs.subtract(rhs); // subtract two fractions
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187 answer = lhs.abs(); // absolute value
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188 answer = lhs.reciprocal(); // reciprocal of lhs</pre>
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189 </div>
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190 </p>
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191 <p>
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192 Like fraction construction, for each of the fraction functions, the resulting fraction is reduced to lowest terms.
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193 </p>
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194 </div>
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195 <div class="section"><h3><a name="a9.3_Fraction_Formatting_and_Parsing"></a>9.3 Fraction Formatting and Parsing</h3>
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196 <p><code>Fraction</code> instances can be converted to and from strings
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197 using the<a href="../apidocs/org/apache/commons/math/fraction/FractionFormat.html">
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198 org.apache.commons.math.fraction.FractionFormat</a> class.
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199 <code>FractionFormat</code> is a <code>java.text.Format</code>
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200 extension and, as such, is used like other formatting objects (e.g.
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201 <code>java.text.SimpleDateFormat</code>):
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202 <div class="source"><pre>FractionFormat format = new FractionFormat(); // default format
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203 Fraction f = new Fraction(2, 4);
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204 String s = format.format(f); // s contains "1 / 2", note the reduced fraction</pre>
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205 </div>
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206 </p>
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207 <p>
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208 To customize the formatting output, one or two
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209 <code>java.text.NumberFormat</code> instances can be used to construct
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210 a <code>FractionFormat</code>. These number formats control the
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211 formatting of the numerator and denominator of the fraction:
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212 <div class="source"><pre>NumberFormat nf = NumberFormat.getInstance(Locale.FRANCE);
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213 // create fraction format with custom number format
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214 // when one number format is used, both numerator and
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215 // denominator are formatted the same
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216 FractionFormat format = new FractionFormat(nf);
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217 Fraction f = new Fraction(2000, 3333);
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218 String s = format.format(c); // s contains "2.000 / 3.333"
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219
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220 NumberFormat nf2 = NumberFormat.getInstance(Locale.US);
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221 // create fraction format with custom number formats
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222 format = new FractionFormat(nf, nf2);
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223 s = format.format(f); // s contains "2.000 / 3,333"</pre>
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224 </div>
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225 </p>
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226 <p>
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227 Formatting's inverse operation, parsing, can also be performed by
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228 <code>FractionFormat</code>. To parse a fraction from a string,
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229 simply call the <code>parse</code> method:
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230 <div class="source"><pre>FractionFormat ff = new FractionFormat();
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231 Fraction f = ff.parse("-10 / 21");</pre>
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232 </div>
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233 </p>
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234 </div>
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235 </div>
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236
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237 </div>
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244 2003-2010
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