# Java常用类之字符串类

**Repository Path**: fpfgitmy_admin/java-used-string

## Basic Information

- **Project Name**: Java常用类之字符串类
- **Description**: 包含了String、StringBuffer、StringBuilder类的简述
- **Primary Language**: Unknown
- **License**: Not specified
- **Default Branch**: master
- **Homepage**: None
- **GVP Project**: No

## Statistics

- **Stars**: 1
- **Forks**: 0
- **Created**: 2021-04-28
- **Last Updated**: 2021-04-28

## Categories & Tags

**Categories**: Uncategorized

**Tags**: None

## README

#### String、StringBuffer、StringBuilder对比
+ String：不可变的字符序列、底层使用不可变的(添加了final)char[]存储
+ StringBuffer：可变的字符序列、线程安全的(效率低)、底层使用可变的(没有添加final)char[]存储
+ StringBuilder：可变的字符序列、线程不安全(效率高)、底层使用可变的(没有添加final)char[]存储

##### 效率对比
```
package com.felixfei.study.test;


/**
 * @describle String、StringBuffer、StringBuilder对比
 */
public class StringBufferBuilderTest {
    /*
    最后结果：

    String拼接用时=1100
    StringBuffer拼接用时=5
    StringBuilder拼接用时=4

    三者效率： StringBuilder > StringBuffer > String
     */
    public static void main(String[] args) {
        long startTime = 0L;
        long endTime = 0L;
        String text = "";
        StringBuffer sb = new StringBuffer("");
        StringBuilder sb1 = new StringBuilder("");

        startTime = System.currentTimeMillis();

        for (int i = 0; i < 20000; i++) {
            text += i;
        }

        endTime = System.currentTimeMillis();
        System.out.println("String拼接用时=" + (endTime - startTime));

        startTime = System.currentTimeMillis();

        for (int i = 0; i < 20000; i++) {
            sb.append(String.valueOf(i));
        }

        endTime = System.currentTimeMillis();
        System.out.println("StringBuffer拼接用时=" + (endTime - startTime));

        startTime = System.currentTimeMillis();

        for (int i = 0; i < 20000; i++) {
            sb1.append(String.valueOf(i));
        }

        endTime = System.currentTimeMillis();
        System.out.println("StringBuilder拼接用时=" + (endTime - startTime));
    }
}

```