2018-09-28

1、static

package staticTest;

public class StaticSub extends StaticSup{
    
    public StaticSub(){
        System.out.println("我是子类");
    }
    static{
        System.out.println("我是子类的static");
    }
    
    public static void main(String[] args){
        new StaticSub();
    }
}


package staticTest;

public class StaticSup {
    
    public StaticSup(){
        System.out.println("我是父类");
    }
    static{
        System.out.println("我是父类的static");
    }
}

运行结果

我是父类的static
我是子类的static
我是父类
我是子类

2、string和StringBuffer

package String;

public class StringTest {
    String str=new String("hello");
    StringBuffer buf=new StringBuffer("hello buffer");
    
    public static void main(String[] args){
        
        StringTest st=new StringTest();
        st.change(st.str);
        st.change2(st.buf);
        System.out.println(st.str);
        System.out.println(st.buf);
    }
    
    public void change(String str){
        str="NewHello";
        System.out.println(str);
    }
    public void change2(StringBuffer buf){
        buf.append("  newBuffer");
    }
}

运行结果

NewHello
hello
hello buffer   newBuffer

3、运行时异常