java字符串拼接常用方式

方式一：+

“+”，是java操作运算符比较常用的，也是简单直接的一种方式。

     String aa = "魅言倾馨";String bb = "子非我鱼";System.out.println(aa+bb);

方式二：StringBuilder.append()和StringBuffer.append()

先有StringBuffer后有StringBuilder，两者就像是孪生双胞胎，该有的都有，只不过大哥StringBuffer，大部分方法都经过synchronized修饰，所以StringBuffer是线程安全的，但是它效率就相对StringBuilder较低

     String aa = "魅言倾馨";String bb = "子非我鱼";StringBuilder sber = new StringBuilder();StringBuffer sbf = new StringBuffer();sber.append(aa).append(bb);System.out.println(sber.toString());sbf.append(aa).append(bb);System.out.println(sbf.toString());

方式三：String类下的cocat()方法

如果拼接的字符串是null，concat会抛出NullPointerException。如果拼接的字符串是一个空字符串（“”），那么concat的效率要更高。如果拼接的字符串非常多，concat的效率就会下降，因为创建的字符串对象越多，开销越大。

         String aa = "魅言倾馨";String bb = "子非我鱼";String concat = aa.concat(bb);System.out.println(concat);

方式四：String类下的join()方法

JDK1.8提供了一种新的字符串拼接姿势：String类增加了一个静态方法join，第一个参数为字符串连接符

     String aa = "魅言倾馨";String bb = "子非我鱼";String join = String.join("-", aa, bb);System.out.println(join);

方式五：StringJoiner

StringJoiner是JDK1.8，java.util包中的一个类，用于构造一个由分隔符重新连接的字符序列

     String aa = "魅言倾馨";String bb = "子非我鱼";StringJoiner sj = new StringJoiner(":", "[", "]");sj.add(aa).add(bb);System.out.println(sj.toString());

StringJoiner源码

package java.util;public final class StringJoiner {private final String prefix;//前缀private final String delimiter;//间隔符private final String suffix;//后缀private StringBuilder value;//值private String emptyValue;//空值public StringJoiner(CharSequence delimiter) {this(delimiter, "", "");//默认前缀和后缀为"",重载调用}public StringJoiner(CharSequence delimiter,CharSequence prefix,CharSequence suffix) {//间隔符，前缀和后缀判断是否为null，null将抛出异常Objects.requireNonNull(prefix, "The prefix must not be null");Objects.requireNonNull(delimiter, "The delimiter must not be null");Objects.requireNonNull(suffix, "The suffix must not be null"); // 成员变量赋值this.prefix = prefix.toString();this.delimiter = delimiter.toString();this.suffix = suffix.toString();this.emptyValue = this.prefix + this.suffix;//空值被设置为只有前后缀}//设置空值，检查是否为nullpublic StringJoiner setEmptyValue(CharSequence emptyValue) {this.emptyValue = Objects.requireNonNull(emptyValue,"The empty value must not be null").toString();return this;}@Overridepublic String toString() {if (value == null) {return emptyValue;//没有值将返回空值或者后续设置的空值} else {if (suffix.equals("")) {return value.toString();//后缀为""直接返回字符串，不用添加} else {//后缀不为""，添加后缀，然后直接返回字符串，修改长度int initialLength = value.length();String result = value.append(suffix).toString();// reset value to pre-append initialLengthvalue.setLength(initialLength);return result;}}}初始化，先添加前缀，有了之后每次先添加间隔符，StringBuilder后续append字符串public StringJoiner add(CharSequence newElement) {prepareBuilder().append(newElement);return this;}//合并StringJoiner，注意后面StringJoiner 的前缀就不要了，后面的appen进来public StringJoiner merge(StringJoiner other) {Objects.requireNonNull(other);if (other.value != null) {final int length = other.value.length();// lock the length so that we can seize the data to be appended// before initiate copying to avoid interference, especially when// merge 'this'StringBuilder builder = prepareBuilder();builder.append(other.value, other.prefix.length(), length);}return this;}//初始化，先添加前缀，有了之后每次先添加间隔符private StringBuilder prepareBuilder() {if (value != null) {value.append(delimiter);} else {value = new StringBuilder().append(prefix);}return value;}public int length() {// Remember that we never actually append the suffix unless we return// the full (present) value or some sub-string or length of it, so that// we can add on more if we need to.//不忘添加后缀的长度return (value != null ? value.length() + suffix.length() :emptyValue.length());}
}

方式六：StringUtils.join()

实战项目中，我们处理字符串的时候，经常会用到这个类.org.apache.commons.lang3.StringUtils包下，该方法更善于拼接数组中的字符串，并且不用担心 NullPointerException。

         String aa = "魅言倾馨";String bb = "子非我鱼";String ids[] = {"1","2","3"};System.out.println(StringUtils.join(aa,bb));String join1 = StringUtils.join(ids,",");System.out.println(join1);

总结

以上所述是小编给大家介绍的Java 字符串拼接姿势，希望对大家有所帮助，如果大家有任何疑问请给我留言，小编会及时回复大家的