public StringBuffer()

public StringBuffer(int capacity)

public StringBuffer(String str)

package com.xuweiwei;

public class StringBufferDemo {
    public static void main(String[] args) {
        //public StringBuffer()
        StringBuffer sb = new StringBuffer();
        System.out.println("sb:"+sb);
        System.out.println("sb的容量："+sb.capacity());
        System.out.println("sb的长度："+sb.length());

        //public StringBuffer(int capacity)
        StringBuffer sb2 = new StringBuffer(50);
        System.out.println("sb2:"+sb2);
        System.out.println("sb2的容量："+sb2.capacity());
        System.out.println("sb2的长度："+sb2.length());

        //public StringBuffer(String str)
        StringBuffer sb3 = new StringBuffer("hello");
        System.out.println("sb3:"+sb3);
        System.out.println("sb3的容量："+sb3.capacity());
        System.out.println("sb3的长度："+sb3.length());


    }
}

public StringBuffer append(String str)

public StringBuffer insert(int offset,String str)

package com.xuweiwei;

public class StringBufferDemo2 {
    public static void main(String[] args) {
        StringBuffer sb = new StringBuffer();
        //public StringBuffer append(String str)
        sb.append("hello");
        sb.append(true);
        sb.append(12);
        sb.append(‘a‘);

        System.out.println("sb:" + sb);

        sb.insert(0,‘d‘);
        System.out.println("sb:" + sb);

    }
}

public StringBuffer deleteCharAt(int index)

public StringBuffer delete(int start,int end)

package com.xuweiwei;

public class StringBufferDemo2 {
    public static void main(String[] args) {
        StringBuffer sb = new StringBuffer();
        sb.append("hello");
        sb.append(true);
        sb.append(12);
        sb.append(‘a‘);
        sb.insert(0, ‘d‘);

        System.out.println("sb:"+sb);
        sb.deleteCharAt(0);
        System.out.println("sb:"+sb);

        sb.delete(1,2);
        System.out.println("sb:"+sb);

    }
}

public StringBuffer replace(int start, int end,String str)

package com.xuweiwei;

public class StringBufferDemo2 {
    public static void main(String[] args) {
        StringBuffer sb = new StringBuffer();
        sb.append("hello").append("world").append("java");

        sb.replace(5, 10, "你好啊，世界");

        System.out.println("sb:" + sb);


    }
}

public StringBuffer reverse()

package com.xuweiwei;

public class StringBufferDemo2 {
    public static void main(String[] args) {
        StringBuffer sb = new StringBuffer();
        sb.append("hello").append("world").append("java");


        System.out.println("sb:" + sb.reverse());


    }
}

public String substring(int start)

public String substring(int start,int end)

package com.xuweiwei;

public class StringBufferDemo2 {
    public static void main(String[] args) {
        StringBuffer sb = new StringBuffer();
        sb.append("hello").append("world").append("java");

        System.out.println("sb:" + sb);
        String str = sb.substring(3);
        System.out.println("sb:" + sb);
        System.out.println("str:" + str);

        
    }
}