Google Guava学习计划第一章Guava Utilities—Preconditions_ComparisonChain_Strings_CharMatcher

写这篇文章时，头有点晕晕的，在一首天空之城下勉强写完。

主要内容如下:

1.preconditions 断言:在类似于条件解析时，进行一些重要的验证,验证为空。2.ComparisonChain 编写比较器：采用ComparisonChain 以total,input,name 三者来排序,按照先后顺序3.Strings 字符串的处理   repeat padEnd padStart  commonPrefix  commonsuffix4.CharMatcher 字符的处理   removeFrom  retainFrom

以下是具体代码：

package Utilities;import com.google.common.base.CharMatcher;import com.google.common.base.Preconditions;import com.google.common.base.Strings;import com.google.common.collect.ComparisonChain;import com.google.common.collect.Lists;import com.google.common.collect.Sets;import org.junit.Test;import java.util.ArrayList;import java.util.List;import java.util.TreeSet;import static org.hamcrest.core.IsEqual.equalTo;import static org.junit.Assert.assertThat;import static org.junit.Assert.assertTrue;/** * ${DESCRIPTION} * 1.preconditions 断言:在类似于条件解析时，进行一些重要的验证,验证为空。 * 2.ComparisonChain 编写比较器 * 3.Strings 字符串的处理 * 4.CharMatcher 字符的处理 * @author mengxp * @version 1.0 * @create 2017-12-11 19:50 **/public class Preconditions_ComparisonChain_Strings_CharMatcher {    //1.***********preconditions*******    @Test    public void testPreconditions_NotNull(){        List<String> var1=null;        Preconditions.checkNotNull(var1,"Collection should  not  be nullable...",var1);    }    @Test    public void testPreconditions_checkArgument(){        final String num="132";        Preconditions.checkArgument(num.equals("133"),"must be equals",num);    }    //检查数组的角标越界    @Test    public void testPreconditions_checkElementIndex(){        Preconditions.checkElementIndex(2,3,"max length is=2");    }    //3.************Strings********    @Test    public void testStringsRepeat(){        String var="mengxp";        String repeat = Strings.repeat(var, 2);        assertThat(repeat,equalTo("mengxpmengxp"));        String commonPrefix= Strings.commonPrefix("AAASS", "AAWW");        assertThat(commonPrefix,equalTo("AA"));        String commonSuffix= Strings.commonSuffix("AAASS", "AAWWSSS");        assertThat(commonSuffix,equalTo("SS"));        // padEnd(String string, int minLength, char padChar) 中minLength为结果的字符串的长度=string+(minlength-原stringLength)*padChar        String padEnd= Strings.padEnd("Jone", 6, 'x');        String padStart= Strings.padStart("78", 4, '0');        String empty= Strings.nullToEmpty(null);        assertThat(empty,equalTo(""));        String nulll = Strings.emptyToNull("");        assertThat(nulll,equalTo(null));        assertTrue(Strings.isNullOrEmpty(""));    }    //4.************CharMatcher 字符的处理************    @Test    public void testCharMatcher(){        assertThat(CharMatcher.javaDigit().matches('1'),equalTo(true));        //获取字符串中某个字符的个数        assertThat(CharMatcher.is('A').countIn("mengxp is good boy .got AAAAA"),equalTo(5));        assertThat(CharMatcher.breakingWhitespace().collapseFrom("meng xiao peng",'*'),equalTo("meng*xiao*peng"));        assertThat(CharMatcher.javaDigit().or(CharMatcher.whitespace()).removeFrom("hello 123 world"),equalTo("helloworld"));        assertThat(CharMatcher.javaDigit().or(CharMatcher.whitespace()).retainFrom("hello 123 world"),equalTo(" 123 "));    }    /**     * 2.ComparisonChain 编写比较器     */    static class ComparisonChainObj implements Comparable<ComparisonChainObj>{        private int total;        private int input;        private int output;        private String name;        public ComparisonChainObj(int input, int output, String name) {            this.input = input;            this.output = output;            this.total=input-output;            this.name = name;        }        public int getTotal() {            return total;        }        public void setTotal(int total) {            this.total = total;        }        public int getInput() {            return input;        }        public void setInput(int input) {            this.input = input;        }        public int getOutput() {            return output;        }        public void setOutput(int output) {            this.output = output;        }        public String getName() {            return name;        }        public void setName(String name) {            this.name = name;        }        @Override        public boolean equals(Object o) {            if (this == o) return true;            if (o == null || getClass() != o.getClass()) return false;            ComparisonChainObj that = (ComparisonChainObj) o;            if (total != that.total) return false;            if (input != that.input) return false;            if (output != that.output) return false;            return name.equals(that.name);        }        @Override        public int hashCode() {            int result = total;            result = 31 * result + input;            result = 31 * result + output;            result = 31 * result + name.hashCode();            return result;        }        //采用ComparisonChain 以total,input,name 三者来排序,按照先后顺序        @Override        public int compareTo(ComparisonChainObj o) {           return ComparisonChain.start().compare(this.total,o.getTotal())                    .compare(this.input,o.getInput())                    .compare(this.name,o.getName()).result();        }        public static void main(String[] args) {            ComparisonChainObj var1=new ComparisonChainObj(200,100,"x");            ComparisonChainObj var2=new ComparisonChainObj(300,200,"c");            ComparisonChainObj var3=new ComparisonChainObj(300,150,"a");            ComparisonChainObj var4=new ComparisonChainObj(200,150,"d");            ArrayList<ComparisonChainObj> objs = Lists.newArrayList(var1, var2, var3, var4);            Preconditions.checkNotNull(objs);            TreeSet<ComparisonChainObj> comparisonChainObjs = Sets.newTreeSet(objs);            System.out.println(comparisonChainObjs);        }    }}
还是那句话，不要为了用guava而去用，根据需要来使用吧。