Java Thread setPriority()方法

Thread類的setPriority()方法用於設定更改執行緒的優先順序。每個執行緒都有一個優先順序，由1到10之間的整數表示。

Thread類提供3個常數屬性:

• public static int MIN_PRIORITY:它是執行緒的最大優先順序，它的值是1。
• public static int NORM_PRIORITY:這是執行緒的普通優先順序，它的值是5。
• public static int MAX_PRIORITY:它是執行緒的最小優先順序，它的值是10。

還可以將執行緒的優先順序設定在1到10之間。此優先順序稱為自定義優先順序或使用者定義的優先順序。

語法

• a:將此執行緒設定為優先順序。

異常

• IllegalArgumentException:如果優先順序不在MIN_PRIORITY到MAX_PRIORITY的範圍內，則丟擲此異常。
• SecurityException:如果當前執行緒無法修改此執行緒，則丟擲此異常。

範例一 :最大優先順序執行緒

public class JavaSetPriorityExp1 extends Thread  
{    
    public void run()  
    {    
        System.out.println("Priority of thread is: "+Thread.currentThread().getPriority());    
    }    
    public static void main(String args[])  
    {    
        // creating one thread   
        JavaSetPriorityExp1 t1=new JavaSetPriorityExp1();    
        // print the maximum priority of this thread  
        t1.setPriority(Thread.MAX_PRIORITY);    
        // call the run() method  
        t1.start();    
    }    
}

執行上面範例程式碼，得到以下結果:

Priority of thread is: 10

範例二 :最小優先順序執行緒

public class JavaSetPriorityExp2 extends Thread  
{    
    public void run()  
    {    
        System.out.println("Priority of thread is: "+Thread.currentThread().getPriority());    
    }    
    public static void main(String args[])  
    {    
        // creating one thread   
        JavaSetPriorityExp2 t1=new JavaSetPriorityExp2();    
        // print the minimum priority of this thread  
        t1.setPriority(Thread.MIN_PRIORITY);    
        // This will call the run() method  
        t1.start();    
    }    
}

執行上面範例程式碼，得到以下結果:

Priority of thread is: 1

範例三 ：正常優先順序執行緒

public class JavaSetPriorityExp3 extends Thread  
{    
    public void run()  
    {    
        System.out.println("Priority of thread is: "+Thread.currentThread().getPriority());    
    }    
    public static void main(String args[])  
    {    
        // creating one thread   
        JavaSetPriorityExp3 t1=new JavaSetPriorityExp3();    
        // print the normal priority of this thread  
        t1.setPriority(Thread.NORM_PRIORITY);    
        // starting the thread   
        t1.start();    
    }    
}

執行上面範例程式碼，得到以下結果:

Priority of thread is: 5

範例四 ：使用者定義優先順序執行緒

public class JavaSetPriorityExp4 extends Thread  
{    
    public void run()  
    {    
        System.out.println("running...");    
    }    
    public static void main(String args[])  
    {    
        // creating one thread   
        JavaSetPriorityExp4 t1=new JavaSetPriorityExp4();    
        JavaSetPriorityExp4 t2=new JavaSetPriorityExp4();  
        // set the priority  
        t1.setPriority(4);  
        t2.setPriority(7);  
        // print the user defined priority   
        System.out.println("Priority of thread t1 is: " + t1.getPriority()); //4  
        System.out.println("Priority of thread t2 is: " + t2.getPriority()); //7  
        // this will call the run() method  
        t1.start();  
    }  
}

執行上面範例程式碼，得到以下結果:

Priority of thread t1 is: 4
Priority of thread t2 is: 7
running...

範例五 ：當優先順序大於10時

public class JavaSetPriorityExp5 extends Thread  
{    
    public void run()  
    {    
        System.out.println("running...");    
    }    
    public static void main(String args[])  
    {    
        // creating one thread   
        JavaSetPriorityExp5 t1=new JavaSetPriorityExp5();    
        JavaSetPriorityExp5 t2=new JavaSetPriorityExp5();  
        // set the priority  
        t1.setPriority(12);  
        t2.setPriority(7);  
        // print exception because priority of t1 is greater than 10  
        System.out.println("Priority of thread t1 is: " + t1.getPriority());   
        System.out.println("Priority of thread t2 is: " + t2.getPriority());   
        // call the run() method  
        t1.start();  
    }  
}

執行上面範例程式碼，得到以下結果:

Exception in thread "main" java.lang.IllegalArgumentException
    at java.lang.Thread.setPriority(Thread.java:1089)
    at JavaSetPriorityExp5.main(JavaSetPriorityExp5.java:13)