public class TestPart {
    
    class A {
    }

    @Inject
    IEclipseContext ctx;
    
    int i;
    
    @Inject
    public TestPart(IEclipseContext ctx) {
        ctx.set(A.class, new A()); // 1
    }

    @Inject
    private void reinjectMe(A a) {
        System.out.println("Injected instance of A: " + a);
    }

    @PostConstruct
    public void createUI(Composite parent) {
        Button btn = new Button(parent, SWT.PUSH);
        btn.setText("test");
        btn.addSelectionListener(new SelectionAdapter() {
            
            @Override
            public void widgetSelected(SelectionEvent e) {
                if(i==0) {
                    ctx.set(A.class, new A()); // 2
                    ++i;
                } else {
                    ctx.remove(A.class); // 3
                }
            }
        });
    }
}

Injected instance of A: TestPart$A@1d51055 // 1
Injected instance of A: TestPart$A@b6377c // 2

// 3
!ENTRY org.eclipse.e4.core 4 0 2013-12-17 09:40:15.378
!MESSAGE Unable to process "TestPart#reinjectMe()": no actual value was found for the argument "A".