在Java中如何避免创建不必要的对象

目录

• 简介
• 1、String和Boolean
• 2、自动拆箱和装箱
• 3、正则表达式
• 总结

// 每次都会创建一个新的String对象，且不会加入常量池
String name2 = new String("李子捌");

// 正确写法
String name1 = "李子捌";

// StringBuffer中的append()方法
public synchronized StringBuffer append(String str) {
    toStringCache = null;
    super.append(str);
    return this;
}

// StringBuilder中的append()方法
public StringBuilder append(String str) {
    super.append(str);
    return this;
}

public static final Boolean TRUE = new Boolean(true);

public static final Boolean FALSE = new Boolean(false);

long start = System.currentTimeMillis();
Integer sum = 0;
for (int i = 0; i <100000; i++) {
    sum += i;
}
System.out.println(System.currentTimeMillis() - start);

long start = System.currentTimeMillis();
// 修改Integer 为 int 
int sum = 0;
for (int i = 0; i <100000; i++) {
    sum += i;
}
System.out.println(System.currentTimeMillis() - start);

public static void main(String[] args) {

    String email = "1057301174@qq.com";
    String regex = "^([a-z0-9A-Z]+[-|.]&＃63;)+[a-z0-9A-Z]@([a-z0-9A-Z]+(-[a-z0-9A-Z]+)&＃63;.)+[a-zA-Z]{2,}$";

    long start = System.currentTimeMillis();
    for (int i = 0; i <10000; i++) {
        email.matches(regex);
    }

    System.out.println(System.currentTimeMillis() - start);

}

public static void main(String[] args) {

    String email = "1057301174@qq.com";
    String regex = "^([a-z0-9A-Z]+[-|.]&＃63;)+[a-z0-9A-Z]@([a-z0-9A-Z]+(-[a-z0-9A-Z]+)&＃63;.)+[a-zA-Z]{2,}$";
    Pattern pattern = Pattern.compile(regex);

    long start = System.currentTimeMillis();
    for (int i = 0; i <10000; i++) {
        //email.matches(regex);
        pattern.matcher(email);
    }

    System.out.println(System.currentTimeMillis() - start);

}