在ecliipse-->preference-->Java--->Debug 設置

Suspend execution:
只保留 suspend for breakpoint.

Hot code replace
保留: show error when hot code replace failed.
          show error when obsolete code remain after replace.
          replace classfiles containing compilation errors.

Communication:
change Debugger timer  to 30000
Launch timer to 200000

The project was not built since its build path is incomplete. The project was not built since its build path is incomplete. Fix the build path then try building this project
The type java.lang.Object cannot be resolved. It is indirectly referenced from required .class files

出現以上訊息的原因是因為你裝了多個版本的jre或jdk的關係。本來Eclipse在建立專案時，會自動參照你的jre路徑，但多個版本就沒辦法了。
你只能手動建立…
1. 進入window\preferences\java\Installed JREs
1)按Add
2)輸入JRE Name, 例JDK1.5.0.03
3)JRE home directory, 選擇安裝的路徑
4)按OK
2. 進入Project\properties\Java Bulid Path
1)Add library
2)選JRE System Library後按Next
3)選workplace default JRE後按finish...

I composed a code as below:

package duanbo;

public class HelloWorld
{
        public static void main(String arg[])
        {
            System.out.println("Hello World");
        }

}

The HelloWorld.java was put on root of E: , I excuse the compile/run process :

The first step was ok. And throw out "Exception in thread "main" java.lang.NoClassDefFoundError: HelloWorld (wrong name: duanbo/HelloWorld)" at step 2.

I think may be I should move the HelloWorld.class to E:\duanbo. So did it.

Redo the up steps. The erroe was same as before.

After some search, I got the right command.




You could add this parameter to find how java class loader work .

javac -verbose classname.java
java -verbose classname


Under no circumstance, I think, you could speak that :" the java HelloWorld sample is easy."
We could study a lot in this lesson.

Let me demo the right code firstly.

public class HelloWorld
{
        public static void main(String arg[])
        {
            System.out.println("Hello World");
        }

}

You should advance some questions about it, or you ...

1. can the "public" keyword be skip?
2. can we change the "String arg[]" parameter to "int arg[]"?
3. does the "void" phrase could be put befor "static", as "public void static mian(String arg[])" ?
4. could the "arg[]" be modified to other name ?

Please find the answer to them with search engine.

Study tha adapter pattern this morning. Found some tutorial are not as good as I imaged.

I parse my code about the adapter to demo it.

Firstly, the object adapter:

And the second demo: Class Adapter:

package duanbo.patterns.adapter;

public class ClassAdapter extends RoundPeg implements ISquarePeg
{
    private RoundPeg roundPeg;

    public ClassAdapter(RoundPeg peg)
    {
        this.roundPeg = peg;
    }

    public void insert(String str)
    {
        roundPeg.insertIntoHole(str);
    }

}

interface IRoundPeg
{
    public void insertIntoHole(String msg);
}

interface ISquarePeg
{
    public void insert(String str);
}

class SquarePeg implements ISquarePeg
{
    public void insert(String str)
    {
        System.out.println("SquarePeg insert():" + str);
    }
}

class RoundPeg implements IRoundPeg
{
    public void insertIntoHole(String msg)
    {
        System.out.println("RoundPeg insertIntoHole():" + msg);
    }
}