String拼接在頻繁使用時，不同方法效能差別較大：

package com.example.ss.hello;

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.widget.TextView;

public class MainActivity extends AppCompatActivity {

    private TextView tv;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        tv = (TextView)findViewById(R.id.hello);
        long n = 10000;

        long start1 = System.currentTimeMillis();
        String s1 = new String("hello");
        for (long i = 0; i < n; i++)
        {
            s1 += "拼接--";
        }
        long end1 = System.currentTimeMillis();
        long time1 = end1 - start1;
        tv.setText("用String+=拼接字串的時間:" + time1);

        long start2 = System.currentTimeMillis();
        String s2 = new String("hello");
        for (long i = 0; i < n; i++)
        {
            s2 = s2 + "拼接--";
        }
        long end2 = System.currentTimeMillis();
        long time2 = end2 - start2;
        tv.append("用String=String+拼接字串的時間" + time2);

        long start3 = System.currentTimeMillis();
        String s3 = new String("hello");
        for (long i = 0; i < n; i++)
        {
            s3 = s3.concat("拼接--");
        }
        long end3 = System.currentTimeMillis();
        long time3 = end3 - start3;
        tv.append("用String.concat拼接字串的時間" + time3);

        long start4 = System.currentTimeMillis();
        StringBuffer s4 = new StringBuffer("hello");
        for (long i = 0; i < n; i++)
        {
            s4.append("拼接--");
        }
        long end4 = System.currentTimeMillis();
        long time4 = end4 - start4;
        tv.append("用StringBuffer.append拼接字串的時間" + time4);

        long start5 = System.currentTimeMillis();
        StringBuilder s5 = new StringBuilder("hello");
        for (long i = 0; i < n; i++)
        {
            s5.append("拼接--");
        }
        long end5 = System.currentTimeMillis();
        long time5 = end5 - start5;
        tv.append("用StringBuilder.append拼接字串的時間" + time5);
    }
}
 

真機執行結果如下

可見使用+= 與使用StringBuilder.append差別達到了指數級。

頻繁使用拼接的操作中若使用+=，則有可能造成頻繁GC，從而產生丟幀的現象。