先上結(jié)果

以上進行了兩組測試（數(shù)據(jù)均來自真機測試）

放大一下stringBuffer和stringBuilder這兩組數(shù)據(jù)

以上不難看出StringBuilder的性能明顯優(yōu)于StringBuffer

以上可以看出不考慮線程安全等因素下耗時如下

StringBuilder耗時>StringBuffer耗時>String耗時>String.format耗時

粗略的解釋一下為什么

• 先說一下正常的字符串相“+”和“.format”之間的區(qū)別
  .format在很多地方都有，主要用途是進行格式化的作用因此使用下面代碼格式化肯定是沒有直接疊加快的

s = String.format("%s%s", s1, s2);

• 在說一下啊說找一下String為什么慢
  首先我們要知道String類是不可變類（String.format就不用說了本身就是String類的方法）而StringBuilder和StringBuffer是可變的
  

  String
  
  
  StringBuilder和StringBuffer
  
  所以StringBuilder和StringBuffer優(yōu)于String因為String疊加需要重新獲取一塊內(nèi)存然后講兩段字符串相加在放入新的內(nèi)存中
  因此StringBuilder和StringBuffer可以明顯在上面的柱狀圖總看出他倆比較牛逼

• 在分析一下StringBuilder和StringBuffer
  小提示：StringBuffer 是線程安全的而StringBuilder并不是！??！
  StringBuffer的所有公開方法都是同步的，StringBuilder是沒有對方法加鎖同步的。
  所以理論上毫無疑問，StringBuilder 的性能要遠大于 StringBuffer。

StringBuffer 和 StringBuilder 的區(qū)別
https://blog.csdn.net/changgebuyu/article/details/86523998

寫一下我測試的代碼

• activity_main.xml

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <GridView
        android:id="@+id/list"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:numColumns="5">
    </GridView>

</LinearLayout>

• MainActivity

package com.hrk.stringtest;

import androidx.appcompat.app.AppCompatActivity;

import android.os.Bundle;
import android.widget.ArrayAdapter;
import android.widget.GridView;

import java.text.DecimalFormat;
import java.util.ArrayList;
import java.util.Random;

public class MainActivity extends AppCompatActivity {
    private ArrayList arrayList;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        arrayList = new ArrayList<String>();
        arrayList.add("");
        arrayList.add("String");
        arrayList.add("stringBuffer");
        arrayList.add("stringBuilder");
        arrayList.add("string.format");
        addList(100, 200);
        addList(100, 500);
        addList(100, 1000);
        addList(10, 200);
        addList(10, 500);
        addList(10, 1000);
        GridView gridView = findViewById(R.id.list);
        gridView.setAdapter(new ArrayAdapter(this, R.layout.list_item, arrayList));
    }

    void addList(int length, int endLength) {
        arrayList.add("疊加到 " + endLength + "(長度：" + length + ")");
        String s = getRandomString(100);
        int num = endLength / length;
        arrayList.add(stringTest(num, s));
        arrayList.add(stringBufferTest(num, s));
        arrayList.add(stringBuilderTest(num, s));
        arrayList.add(stringFormatTest(num, s));
    }

    String stringTest(int num, String s) {
        long start = System.nanoTime();
        String ends;
        for (int i = 0; i < 100; i++) {
            ends = "";
            for (int j = 0; j < num; j++) {
                ends += s;
            }

        }
        long end = System.nanoTime();
        DecimalFormat df = new DecimalFormat("0.000");
        return df.format(Double.valueOf(end - start) / (100 * 1000 * 1000));
    }

    String stringBufferTest(int num, String s) {
        long start = System.nanoTime();
        StringBuffer stringBuffer = new StringBuffer(s);
        StringBuffer endStringBuffer;
        for (int i = 0; i < 100; i++) {
            endStringBuffer = new StringBuffer();
            for (int j = 0; j < num; j++) {
                endStringBuffer.append(stringBuffer);
            }
        }
        long end = System.nanoTime();
        DecimalFormat df = new DecimalFormat("0.000");
        return df.format(Double.valueOf(end - start) / (100 * 1000 * 1000));
    }


    String stringBuilderTest(int num, String s) {
        long start = System.nanoTime();
        StringBuilder stringBuilder = new StringBuilder(s);
        StringBuilder endStringBuilder;
        for (int i = 0; i < 100; i++) {
            endStringBuilder = new StringBuilder();
            for (int j = 0; j < num; j++) {
                endStringBuilder.append(stringBuilder);
            }
        }
        long end = System.nanoTime();
        DecimalFormat df = new DecimalFormat("0.000");
        return df.format(Double.valueOf(end - start) / (100 * 1000 * 1000));
    }

    String stringFormatTest(int num, String s) {
        long start = System.nanoTime();
        String ends;
        for (int i = 0; i < 100; i++) {
            ends = "";
            for (int j = 0; j < num; j++) {
                ends = String.format("%s%s", ends, s);
            }
        }
        long end = System.nanoTime();
        DecimalFormat df = new DecimalFormat("0.000");
        return df.format(Double.valueOf(end - start) / (100 * 1000 * 1000));
    }

    public static String getRandomString(int length) {
        String str = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";
        Random random = new Random();
        StringBuffer sb = new StringBuffer();
        for (int i = 0; i < length; i++) {
            int number = random.nextInt(62);
            sb.append(str.charAt(number));
        }
        return sb.toString();
    }
}

• list_item.xml

<?xml version="1.0" encoding="UTF-8"?>
<TextView
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/text1"
    android:textSize="8dp"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"/>