String中trim()方法作用
輸入參數爲null時返回null,否則去除掉字符串兩邊的空格或者製表符
測試
public class TrimTest {
public static void main(String[] args) {
String st1 = "";
String st2= "hello word ";
String st3 = " hello word";
String st4 =" hello word ";
System.out.println("st1:" + st1.trim());
System.out.println("st2:" + st2.trim());
System.out.println("st3:" + st3.trim());
System.out.println("st4:" + st4.trim() +"!!!");
}
}
輸出結果:
st1:
st2:hello word
st3:hello word
st4:hello word!!!
源碼:
可以看到源碼中是通過判斷字符串前和後面的空格長度,然後進行截取
public String trim() {
int len = value.length;
int st = 0;
char[] val = value;
while ((st < len) && (val[st] <= ' ')) {
st++;
}
while ((st < len) && (val[len - 1] <= ' ')) {
len--;
}
return ((st > 0) || (len < value.length)) ? substring(st, len) : this;
}
如果輸入的是空字符串,會報空指針錯誤
String st1 = null;
System.out.println("st1:" + st1.trim());
報錯: