public String buildString(List<String> stringList, String delimiter){
StringBuilder builder = new StringBuilder();
for (String s : stringList) {
if(s !=null){
builder.append(s).append(delimiter);
}
}
builder.setLength(builder.length() – delimiter.length());
return builder.toString();
}
注意要删除在最后面的分隔符。不是很难懂，但是使用Joiner类可以得到简单的代码模板。同样的例子使用Joiner类代码如下：
public String buildString(List<String> stringList, String delimiter){
return Joiner.on(delimiter).skipNulls().join(stringList);
}
这样更加简明并且不会出错。如果你想将null值替换掉，可以使用如下方法：
Joiner.on("|").useForNull("no value").join(stringList);
使用Joiner类有几点需要注意。Joiner类不仅仅可以处理字符串的array、list、iterable，他还可以处理任何对象的array、list、iterable。结果就是调用每一个元素的toString()方法。因此，如果没有使用skipNulls或者useForNull，就会抛出空指针异常。Joiner对象一旦被创建就是不可变的，所以他们是线程安全的，可以被当作常亮来看待。然后看看下面的代码片段：
Joiner stringJoiner = Joiner.on("|").skipNulls();
//使用useForNull方法将会返回一个新的Joiner实例
stringJoiner.useForNull("missing");
stringJoiner.join("foo","bar",null);
在上面的代码实例当中，useForNull方法并没有起作用，null值仍然报NPE了。
StringBuilder stringBuilder = new StringBuilder();
Joiner joiner = Joiner.on("|").skipNulls();
//返回的StringBuilder实例当中包含连接完成的字符串
joiner.appendTo(stringBuilder,"foo","bar","baz");
上面的例子，我们传入一个StringBuilder的参数并且返回一个StringBuilder实例。
FileWriter fileWriter = new FileWriter(new File("path")):
List<Date> dateList = getDates();
Joiner joiner = Joiner.on("#").useForNulls(" ");
// 返回由字符串拼接后的FileWriter实例
joiner.appendTo(fileWriter,dateList);
这是一个与上一个相似的例子。我们传入一个FileWriter实例和一组数据，就会将这组数据拼接后附加到FileWriter当中并且返回。
MapJoiner mapJoiner = Joiner.on("#").withKeyValueSeparator("=");
快速回顾一下上面内容：
@Test
public void testMapJoiner() {
String expectedString = "Washington D.C=Redskins#New York City=Giants#Philadelphia=Eagles#Dallas=Cowboys";
Map<String,String> testMap = Maps.newLinkedHashMap();
testMap.put("Washington D.C","Redskins");
testMap.put("New York City","Giants");
testMap.put("Philadelphia","Eagles");
testMap.put("Dallas","Cowboys");
String returnedString = Joiner.on("#"). withKeyValueSeparator("=").join(testMap);
assertThat(returnedString,is(expectedString));
}
回顾时间
String testString = "Monday,Tuesday,,Thursday,Friday,,";
//parts is [Monday, Tuesday, , Thursday,Friday]
String[] parts = testString.split(",");
可以看到，String.split方法省略了最后的2个空串。在有些时候，这个做法是你需要的，但是这些事情是应该由程序员来决定是否省略。Splitter类可以帮助我们实现与Joiner类相反的功能。Splitter可以使用单个字符、固定字符串、正则表达式串、正则表达式对象或者CharMatcher对象（另一个Guava的类，本章会讲到）来分割字符串。可以给定具体分割符来创建Splitter对象然后使用。一旦拥有了Splitter实例后就可以调用split方法，并且会返回包含分割后字符串的迭代器对象。
Splitter.on(‘|‘).split("foo|bar|baz");
Splitter splitter = Splitter.on("\\d+");
在上面的例子当中，我们看到一个Splitter 实例使用了‘|‘字符分割，另外一个实例使用了正则表达式进行分割。
//Splits on ‘|‘ and removes any leading or trailing whitespace Splitter splitter = Splitter.on(‘|‘).trimResults();
与Joiner类一样Splitter类同样是一个不可变的类，所以在使用的时候应该使用调用trimResults方法后返回的Splitter实例。
Splitter splitter = Splitter.on(‘|‘);
//Next call returns a new instance, does not
modify the original!
splitter.trimResults();
//Result would still contain empty elements
Iterable<String> parts = splitter.split("1|2|3|||");
Splitter 类，像Joiner与MapJoiner一样也有MapSplitter类。MapSplitter类可以将字符串转换成Map实例返回，并且元素的顺序与字符串给定的顺序相同。使用下面方法构造一个MapSplitter实例：
//MapSplitter is defined as an inner class of Splitter
Splitter.MapSplitter mapSplitter = Splitter.on("#"). withKeyValueSeparator("=");
@Test
public void testSplitter() {
String startString = "Washington D.C=Redskins#New York City=Giants#Philadelphia=Eagles#Dallas=Cowboys";
Map<String,String> testMap = Maps.newLinkedHashMap();
testMap.put("Washington D.C","Redskins");
testMap.put("New York City","Giants");
testMap.put("Philadelphia","Eagles");
testMap.put("Dallas","Cowboys");
Splitter.MapSplitter mapSplitter = Splitter.on("#").withKeyValueSeparator("=");
Map<String,String> splitMap = mapSplitter.split(startSring);
assertThat(testMap,is(splitMap));
}
byte[] bytes = someString.getBytes();
try{
bytes = "foobarbaz".getBytes("UTF-8");
}catch (UnsupportedEncodingException e){
//This really can‘t happen UTF-8 must be supported
}
byte[] bytes2 = "foobarbaz".getBytes(Charsets.UTF_8);
StringBuilder builder = new StringBuilder("foo");
char c = ‘x‘;
for(int i=0; i<3; i++){
builder.append(c);
}
return builder.toString();
Strings.padEnd("foo",6,‘x‘);
CharMatcher.BREAKING_WHITESPACE.replaceFrom(stringWithLinebreaks,‘ ‘);
@Test
public void testRemoveWhiteSpace(){
String tabsAndSpaces = "String with spaces and tabs";
String expected = "String with spaces and tabs";
String scrubbed = CharMatcher.WHITESPACE.collapseFrom(tabsAndSpaces,‘ ‘);
assertThat(scrubbed,is(expected));
}
@Test
public void testTrimRemoveWhiteSpace(){
String tabsAndSpaces = " String with spaces and tabs";
String expected = "String with spaces and tabs";
String scrubbed = CharMatcher.WHITESPACE. trimAndCollapseFrom(tabsAndSpaces,‘ ‘);
assertThat(scrubbed,is(expected));
}
@Test
public void retainFromTest()
{
String lettersAndNumbers = "foo989yxbar234";
String expected = "989234";
String actual = CharMatcher.JAVA_DIGIT.retainFrom(lettersAndNumbers);
assertEquals(expected, actual);
}
CharMatcher cm = CharMatcher.JAVA_DIGIT.or(CharMatcher.WHITESPACE);
if(someObj == null){
throw new IllegalArgumentException(" someObj must not be null");
}
checkNotNull(someObj,"someObj must not be null");
public class PreconditionExample {
private String label;
private int[] values = new int[5];
private int currentIndex;
public PreconditionExample(String label) {
//返回label如果不为空
this.label = checkNotNull(label,"Label can‘‘t be null");
}
public void updateCurrentIndexValue(int index, int valueToSet) {
//检查索引是否有效
this.currentIndex = checkElementIndex(index, values.length, "Index out of bounds for values");
//检查参数值
checkArgument(valueToSet <= 100,"Value can‘t be more than 100");
values[this.currentIndex] = valueToSet;
}
public void doOperation(){
checkState(validateObjectState(),"Can‘t perform operation");
}
private boolean validateObjectState(){
return this.label.equalsIgnoreCase("open") && values[this.
currentIndex]==10;
}
}
public class Book implements Comparable<Book> {
private Person author;
private String title;
private String publisher;
private String isbn;
private double price;
public String toString() {
return Objects.toStringHelper(this).omitNullValues().add("title", title).add("author", author).add("publisher", publisher)
.add("price",price).add("isbn", isbn).toString();
}
｝
String value = Objects.firstNonNull(someString, "default value");
public int hashCode() {
return Objects.hashCode(title, author, publisher, isbn);
}
int result = this.title.compareTo(o.getTitle());
if (result != 0) {
return result;
}
result = this.author.compareTo(o.getAuthor());
if (result != 0) {
return result;
}
result = this.publisher.compareTo(o.getPublisher());
if(result !=0 ) {
return result;
}
return this.isbn.compareTo(o.getIsbn());
}
public int compareTo(Book o) {
return ComparisonChain.start() .compare(this.title, o.getTitle()) .compare(this.author, o.getAuthor())
.compare(this.publisher, o.getPublisher()) .compare(this.isbn, o.getIsbn()) .compare(this.price, o.getPrice()) .result();
}
原文：http://www.cnblogs.com/sunada2005/p/4678942.html