synchronized 的理解

第一種：package?com.ucmed.zsyy.util;

/**

*?Created?by?ucmed?on?2017/2/8.

*/

public?class?DirtyRead?{

private?String?username?=?"zjkj";

private?String?password?=?"123";

public?synchronized?void?setValue(String?username,?String?password)?{

System.out.println("set線程："?+?Thread.currentThread().getPriority());

this.username?=?username;

try?{

Thread.sleep(2000);

}?catch(InterruptedException?e)?{

e.printStackTrace();

}

this.password?=?password;

System.out.println("setValue最終結果：username?=?"?+?username?+?"??,?password?=?"?+?password);

}

public?void?getValue()?{

System.out.println("get線程："?+?Thread.currentThread().getPriority());

System.out.println("getValue最終結果：username?=?"?+?username?+?"??,?password?=?"?+?password);

}

public?static?void?main(String[]?args)?throws?InterruptedException?{

final?DirtyRead?dr?=?new?DirtyRead();

Thread?t1?=?new?Thread(new?Runnable()?{

@Override

public?void?run()?{

dr.setValue("z3",?"456");

}

});

System.out.println("主線程："?+?Thread.currentThread().getPriority());

t1.start();

Thread.sleep(1000);

dr.getValue();

}

}

第二種:

package?com.ucmed.zsyy.util;

/**

*?Created?by?ucmed?on?2017/2/8.

*/

public?class?DirtyRead?{

private?String?username?=?"zjkj";

private?String?password?=?"123";

public?synchronized?void?setValue(String?username,?String?password)?{

System.out.println("set線程："?+?Thread.currentThread().getPriority());

this.username?=?username;

try?{

Thread.sleep(2000);

}?catch(InterruptedException?e)?{

e.printStackTrace();

}

this.password?=?password;

System.out.println("setValue最終結果：username?=?"?+?username?+?"??,?password?=?"?+?password);

}

public?synchronized?void?getValue()?{

System.out.println("get線程："?+?Thread.currentThread().getPriority());

System.out.println("getValue最終結果：username?=?"?+?username?+?"??,?password?=?"?+?password);

}

public?static?void?main(String[]?args)?throws?InterruptedException?{

final?DirtyRead?dr?=?new?DirtyRead();

Thread?t1?=?new?Thread(new?Runnable()?{

@Override

public?void?run()?{

dr.setValue("z3",?"456");

}

});

System.out.println("主線程："?+?Thread.currentThread().getPriority());

t1.start();

Thread.sleep(1000);

dr.getValue();

}

}

理解：

這里只有一個對象，一個對象的多個synchronized修飾的方法的情況

上面例子是當get方法加上鎖后，要等待set方法執行完后再執行

在方法上加synchronized關鍵字，持有的鎖為當前對象，當一個線程調用了其中一個synchronized的方法后，其他線程再調用該類中其他synchronized修飾的方法會掛起等待，需要等上一個線程執行完，釋放鎖后，其他調用線程取得鎖后才會執行

不是多個鎖，是多個synchronized修飾的方法..這些方法是同一個鎖