java_11_classpath

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Project1

package com.pa;

public class JavaA {
    public void hello(){
        System.out.println("my name is A ! ");
    }
    
    public static void main(String[] args) {
        JavaA obj=new JavaA();
        obj.hello();
    }
}

Project2

package com.pb;

import com.pa.JavaA;

public class JavaB {
    public void hello(){
        System.out.println("my name is B ! ");
    }
    
    public static void main(String[] args) {
        JavaA a=new JavaA();
        a.hello();
        
        JavaB b=new JavaB();
        b.hello();
    }
}

Project3

package com.pc;

import com.pa.JavaA;
import com.pb.JavaB;

public class JavaC {
    public void hello(){
        System.out.println("my name is C ! ");
    }
    
    public static void main(String[] args) {
        JavaA a=new JavaA();
        a.hello();
        
        JavaB b=new JavaB();
        b.hello();
        
        JavaC c=new JavaC();
        c.hello();
    }
}

C:\test\java\09_类路径classpath\project2>javac -classpath c:/test com/pb/JavaB.java

C:\test\java\09_类路径classpath\project2>java -classpath ./;c:/test com.pb.JavaB
my name is A !
my name is B !

解析：

java -classpath ./;c:/test com.pb.JavaB

-classpath：指定class的查找路径
./：路径1，当前目录
;：多个路径用分号隔开
c:/test：路径2
com.pb.JavaB：要执行的java类

执行顺序：

1. 先在./当前路径查找com/pb/JavaB.class，能找到
2. JavaB用到了com.pa.JavaA
3. 先再./当前路径查找com/pa/JavaA.class，找不到
4. 再到c:/test路径下查找com/pa/JavaA.class，能找到，执行
5. 若是都找不到，则报错类不存在