Java.包装类.StringBuilder(Buffer)

目录

1.1StringBuilder(单线程)

1.1.1常用的构造方法

1.1.2常用的成员方法

注意

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1.1StringBuilder(单线程)

1.1.1常用的构造方法

方法声明	功能
StringBuilder()	使用无参构造对象，容量为16
StringBuilder(int capacity)	由参数指定类型对象，容量为指定大小
StringBuilder(String str)	由参数指定字符串构造对象，容量为：16+字符串长度

1.1.2常用的成员方法

方法声明	功能
int capacity()	返回对象容量
int length()	返回字符个数
StringBiulder insert(int offset, String str)	插入字符串并返回调用对象
StringBuider deleteCharAt(int index)	删除下标index字符
StringBuilder append(String str)	添加str
StringBuider replace(int start, int end,String str)	替换指定范围字符串
StringBuilder delete(int start,int end)	删除指定范围字符串
StringBuilder reverse()	反转字符串

public class StringBuilderTest {
    public static void main(String[] args){
        StringBuilder stringBuilder1 = new StringBuilder();
        System.out.println(stringBuilder1);//自动调用toString
        System.out.println(stringBuilder1.capacity());// 16
        System.out.println(stringBuilder1.length());// 0
        System.out.println("----------------------");
        StringBuilder stringBuilder2 = new StringBuilder(32);
        System.out.println(stringBuilder2.capacity());// 32
        System.out.println(stringBuilder2.length());//0
        System.out.println("----------------------");
        StringBuilder stringBuilder3 = new StringBuilder("jinyouxin");
        System.out.println(stringBuilder2);
        System.out.println(stringBuilder3.capacity());// 9+16=25
        System.out.println(stringBuilder3.length());//9
        System.out.println("----------------------");
        //区分String 和 StringBuilder
        StringBuilder stringBuilder4 = stringBuilder3.insert(0,"qs");
        System.out.println(stringBuilder4);//qsjinyouxin
        System.out.println(stringBuilder3);//qsjinyouxin
        stringBuilder4.append("cool");
        System.out.println(stringBuilder4);//qsjinyouxincool
        System.out.println("-------------------------");
        String str = "jinyouxin";
        String str_1 = str.toUpperCase();
        System.out.println(str_1);//JINYOUXIN
        System.out.println(str);// jinyouxin
        //String到stringBuilder转换
        String string1 = stringBuilder4.toString();
        StringBuilder stringBuider = new StringBuilder(string1);
        //效率 String

注意

StringBuilder的许多返回值为StringBuilder,return this,目的在于可以连续调用。

StringBuffer(多线程)不安全