System.exit(status);
Runtime.getRuntime().halt(status)

System.exit(status)解釋如下：

Terminates the currently running Java Virtual Machine.
The  argument serves as a status code; 
by convention, a nonzero status code indicates abnormal termination 

終止當(dāng)前正在運(yùn)行的Java虛擬機(jī)。參數(shù)作為狀態(tài)代碼，按照慣例，一個(gè)非零狀態(tài)碼表示異常終止。
用線程描述，在多線程情況下，可能更準(zhǔn)確一些。

1. 調(diào)用方法后，線程會(huì)退出。
2. 未捕獲的異常被線程拋出，但如果有其他非守護(hù)線程，程序?qū)⒗^續(xù)運(yùn)行。
3. 反饋狀態(tài)碼，一般在腳本中有用。
4. 線程退出，還是做一些清理動(dòng)作。

源碼：

/**
     * Terminates the currently running Java virtual machine by initiating its
     * shutdown sequence.  This method never returns normally.  The argument
     * serves as a status code; by convention, a nonzero status code indicates
     * abnormal termination.
     *
     * <p> The virtual machine's shutdown sequence consists of two phases.  In
     * the first phase all registered {@link #addShutdownHook shutdown hooks},
     * if any, are started in some unspecified order and allowed to run
     * concurrently until they finish.  In the second phase all uninvoked
     * finalizers are run if {@link #runFinalizersOnExit finalization-on-exit}
     * has been enabled.  Once this is done the virtual machine {@link #halt
     * halts}.
     *
     * <p> If this method is invoked after the virtual machine has begun its
     * shutdown sequence then if shutdown hooks are being run this method will
     * block indefinitely.  If shutdown hooks have already been run and on-exit
     * finalization has been enabled then this method halts the virtual machine
     * with the given status code if the status is nonzero; otherwise, it
     * blocks indefinitely.
     *
     * <p> The <tt>{@link System#exit(int) System.exit}</tt> method is the
     * conventional and convenient means of invoking this method. <p>
     *
     * @param  status
     *         Termination status.  By convention, a nonzero status code
     *         indicates abnormal termination.
     *
     * @throws SecurityException
     *         If a security manager is present and its <tt>{@link
     *         SecurityManager#checkExit checkExit}</tt> method does not permit
     *         exiting with the specified status
     *
     * @see java.lang.SecurityException
     * @see java.lang.SecurityManager#checkExit(int)
     * @see #addShutdownHook
     * @see #removeShutdownHook
     * @see #runFinalizersOnExit
     * @see #halt(int)
     */
    public void exit(int status) {
        // Make sure we don't try this several times
        synchronized(this) {
            if (!shuttingDown) {
                shuttingDown = true;

                Thread[] hooks;
                synchronized (shutdownHooks) {
                    // create a copy of the hooks
                    hooks = new Thread[shutdownHooks.size()];
                    shutdownHooks.toArray(hooks);
                }

                // Start all shutdown hooks concurrently
                for (Thread hook : hooks) {
                    hook.start();
                }

                // Wait for all shutdown hooks to finish
                for (Thread hook : hooks) {
                    try {
                        hook.join();
                    } catch (InterruptedException ex) {
                        // Ignore, since we are at VM shutdown.
                    }
                }

                // Ensure finalization on exit, if requested
                if (finalizeOnExit) {
                    runFinalization();
                }

                // Get out of here finally...
                nativeExit(status);
            }
        }
    }

Java虛擬機(jī)退出包括兩個(gè)階段：

第一個(gè)階段：會(huì)以某種未指定的順序啟動(dòng)所有已注冊(cè)鉤子，并且允許它們同時(shí)運(yùn)行直至結(jié)束。
第二個(gè)階段：如果已啟用runFinalizersOnExit設(shè)置為true，則運(yùn)行所有未調(diào)用的終結(jié)方法（finalizer方法）。

Runtime.getRuntime().halt(status)解釋如下：

Forcibly terminates the currently running Java virtual machine.  
This method never returns normally. 

現(xiàn)在runtime的halt比較好理解了，他不會(huì)執(zhí)行鉤子函數(shù)和finalizer方法，而是直接退出。

源碼

 /**
     * Forcibly terminates the currently running Java virtual machine.  This
     * method never returns normally.
     *
     * <p> This method should be used with extreme caution.  Unlike the
     * <tt>{@link #exit exit}</tt> method, this method does not cause shutdown
     * hooks to be started and does not run uninvoked finalizers if
     * finalization-on-exit has been enabled.  If the shutdown sequence has
     * already been initiated then this method does not wait for any running
     * shutdown hooks or finalizers to finish their work. <p>
     *
     * @param  status
     *         Termination status.  By convention, a nonzero status code
     *         indicates abnormal termination.  If the <tt>{@link Runtime#exit
     *         exit}</tt> (equivalently, <tt>{@link System#exit(int)
     *         System.exit}</tt>) method has already been invoked then this
     *         status code will override the status code passed to that method.
     *
     * @throws SecurityException
     *         If a security manager is present and its <tt>{@link
     *         SecurityManager#checkExit checkExit}</tt> method does not permit
     *         an exit with the specified status
     *
     * @see #exit
     * @see #addShutdownHook
     * @see #removeShutdownHook
     * @since 1.3
     */
    public void halt(int status) {
        nativeExit(status);
    }