Java StringBuilder setLength()方法及实例

StringBuilder的 setLength(int newLength) 方法是用来 设置字符序列的长度等于newLength 的。如果作为参数传递的newLength小于旧的长度，则旧的长度被改变为newLength。 如果作为参数传递的newLength大于或等于旧的长度，则在旧序列的末尾添加空字符（’\u0000’），这样长度就成为新的长度参数。

语法

public void setLength(int newLength)

参数： 该方法接受一个参数 newLength ，它是一个整数类型的值，指的是你要设置的序列的新长度。
返回： 该方法不返回任何东西。
异常： 如果newLength是负数，则会 出现IndexOutOfBoundsException 下面的程序说明了java.lang.StringBuilder.setLength()方法：

示例1 :

// Java program to demonstrate// the setLength() Method. class GFG {     public static void main(String[] args)    {        // create a StringBuilder object        // with a String pass as parameter        StringBuilder str            = new StringBuilder("WelcomeGeeks");         // print string        System.out.println("String length = "                           + str.length() +                  " and contains = " + str);         // set length equal to 10        str.setLength(10);         // print string        System.out.println("After setLength() String = "                           + str.toString());    }}

输出

String length = 12 and contains = WelcomeGeeksAfter setLength() String = WelcomeGee

例2 :

// Java program to demonstrate// the setLength() Method. class GFG {    public static void main(String[] args)    {         // create a StringBuilder object        // with a String pass as parameter        StringBuilder str            = new StringBuilder("Tony Stark will die");         // print string        System.out.println("String length = "                           + str.length() +           " and contains = \"" + str + "\"");         // set length equal to 25        str.setLength(25);         // print string        System.out.println("After setLength() String = \""                           + str.toString() + "\"");    }}

输出

String length = 19 and contains = "Tony Stark will die"After setLength() String = "Tony Stark will die      "

例3： 当新的长度为负数时。

// Java program to demonstrate// Exception thrown by the setLength() Method. class GFG {    public static void main(String[] args)    {         // create a StringBuilder object        // with a String pass as parameter        StringBuilder str            = new StringBuilder("Tony Stark");         try {            // pass length -15            str.setLength(-15);        }        catch (Exception e) {             e.printStackTrace();        }    }}

输出

java.lang.StringIndexOutOfBoundsException: String index out of range: -15    at java.lang.AbstractStringBuilder.setLength(AbstractStringBuilder.java:207)    at java.lang.StringBuilder.setLength(StringBuilder.java:76)    at GFG.main(File.java:15)

参考文献: https://docs.oracle.com/javase/10/docs/api/java/lang/StringBuilder.html#setLength(int)