java + concat

concat()方法 (concat() method)

• concat() is a method used for concatenation of strings.

  concat()是用于串联字符串的方法。

• We pass only one string argument in concat() and concat it with other string.

  我们仅在concat()中传递一个字符串参数，然后将其与其他字符串连接。

Example:

例：

public class PassingArgument {public static void main(String[] args) {String str = "Java", lang = "Language";
System.out.println(str.concat(lang));
}
}

Output

输出量

D:\Programs>javac PassingArgument.java
D:\Programs>java PassingArgument
JavaLanguage

• We should remember one thing at the time of passing the argument in concat() method. We can only pass a string and if we pass any other type of argument then we will get an error.

  在concat()方法中传递参数时，我们应该记住一件事。 我们只能传递一个字符串，如果我们传递任何其他类型的参数，那么我们将得到一个错误。

• concat() method throws NullPointer Exception when a string is concatenated with 'null'.

  当字符串与'null'连接时， concat()方法将引发NullPointer异常 。

Example:

例：

public class ConcatNull {public static void main(String[] args) {String str1 = "We will get an exception string concatenate with null in case of concat()";
String str2 = null;
// It raises an NullPointer Exception
System.out.println(str1.concat(str2));
}
}

Output

输出量

D:\Programs>javac ConcatNull.java
D:\Programs>java ConcatNull
Exception in thread "main" java.lang.NullPointerException
at java.base/java.lang.String.concat(String.java:1936)
at ConcatNull.main(ConcatNull.java:7)

The performance of concat() is high as compare to '+' because it generates a new object when string length is greater than 0.

与'+'相比， concat()的性能较高，因为它在字符串长度大于0时会生成一个新对象。

'+'运算符 ('+' operator)

• '+' is an operator used for concatenation of strings.

  “ +”是用于字符串连接的运算符。

• We can take any number of strings argument with '+' and merge it with all other strings.

  我们可以将任意数量的字符串参数加'+'并将其与所有其他字符串合并。

Example:

例：

public class PassingArgument {public static void main(String[] args) {String str = "Java", lang = "Language";
System.out.println(str + lang);
}
}

Output

输出量

D:\Programs>javac PassingArgument.java
D:\Programs>java PassingArgument
JavaLanguage

• We don't need to remember anything at the time of passing argument in '+' operator. We can pass any type of argument if we pass other types of argument then we will not get any error.

  在'+'运算符中传递参数时，我们不需要记住任何事情。 如果我们传递其他类型的参数，那么我们可以传递任何类型的参数，那么我们将不会收到任何错误。

• '+' operator doesn't raise an exception when a string is concatenated with 'null'.

  当字符串与'null'连接时， '+'运算符不会引发异常。

Example:

例：

public class ConcatNull {public static void main(String[] args) {String str1 = "We will not get any exception when string concatenate with null in case of '+'";
String str2 = null;
// It will not raises any NullPointer Exception
System.out.println(str1 + str2);
}
}

Output

输出量

D:\Programs>javac ConcatNull.java
D:\Programs>java ConcatNull
We will not get any exception when string concatenate with null in case of '+'null

The performance of '+' operator is low as compare to concat() because it always generates new object whether string length is greater than 0 or less than 0.

与concat()相比， '+'运算符的性能较低，因为无论字符串长度大于0还是小于0，它始终会生成新对象。

翻译自: https://www.includehelp.com/java/differences-between-concat-method-and-plus-operator-in-java.aspx

java + concat